Words that end in -is or -ness tend to maintain the same form for the singular and the plural.
See the full list below:
| Word | Plural |
|---|---|
| series | series |
| fish | fish |
| species | species |
| aircraft | aircraft |
| fig. | fig. |
| sheep | sheep |
| percent | percent |
| dec. | dec. |
| cattle | cattle |
| machinery | machinery |
| folk | folk |
| louis | louis |
| craft | craft |
| ross | ross |
| ms | ms |
| beef | beef |
| salmon | salmon |
| corps | corps |
| oz | oz |
| jacques | jacques |
| offspring | offspring |
| deer | deer |
| kin | kin |
| trout | trout |
| cannon | cannon |
| military | military |
| fair | fair |
| yuan | yuan |
| co. | co. |
| phoenix | phoenix |
| yen | yen |
| col. | col. |
| siemens | siemens |
| sperm | sperm |
| bream | bream |
| gis | gis |
| carp | carp |
| tuna | tuna |
| goldfish | goldfish |
| roach | roach |
| sec | sec |
| chassis | chassis |
| upstairs | upstairs |
| bordeaux | bordeaux |
| grand | grand |
| mc | mc |
| koi | koi |
| oesophagitis | oesophagitis |
| mink | mink |
| rendezvous | rendezvous |
| catfish | catfish |
| para. | para. |
| shrimp | shrimp |
| zebra | zebra |
| chad | chad |
| grouse | grouse |
| prawn | prawn |
| av. | av. |
| downstairs | downstairs |
| spacecraft | spacecraft |
| mackerel | mackerel |
| brit | brit |
| shellfish | shellfish |
| celsius | celsius |
| figs. | figs. |
| fowl | fowl |
| patois | patois |
| haddock | haddock |
| gal | gal |
| detritus | detritus |
| rhubarb | rhubarb |
| vols. | vols. |
| mg/kg | mg/kg |
| forceps | forceps |
| ascites | ascites |
| asparagus | asparagus |
| jus | jus |
| hiatus | hiatus |
| hertz | hertz |
| sec. | sec. |
| ex. | ex. |
| facies | facies |
| macroeconomics | macroeconomics |
| grice | grice |
| antelope | antelope |
| vermin | vermin |
| marlin | marlin |
| rhinoceros | rhinoceros |
| pres | pres |
| moose | moose |
| jun | jun |
| trans | trans |
| swordfish | swordfish |
| gallows | gallows |
| alms | alms |
| plaice | plaice |
| atari | atari |
| poetics | poetics |
| jellyfish | jellyfish |
| woodcock | woodcock |
| eugenics | eugenics |
| camus | camus |
| steelworks | steelworks |
| springbok | springbok |
| corydoras | corydoras |
| agonistes | agonistes |
| ironworks | ironworks |
| nox | nox |
| roux | roux |
| albatross | albatross |
| quail | quail |
| gasworks | gasworks |
| gramps | gramps |
| tsunami | tsunami |
| tench | tench |
| fisa | FISA |
| samurai | samurai |
| spawn | spawn |
| ninja | ninja |
| gross | gross |
| bonsai | bonsai |
| ko | ko |
| waterfowl | waterfowl |
| angelfish | angelfish |
| bison | bison |
| yu | yu |
| pct | pct |
| subspecies | subspecies |
| scampi | scampi |
| badlands | badlands |
| zloty | zloty |
| xu | xu |
| heathen | heathen |
| zhu | zhu |
| bi | bi |
| semi-darkness | semi-darkness |
| chamois | chamois |
| sumo | sumo |
| clownfish | clownfish |
| precis | precis |
| stats | stats |
| wildebeest | wildebeest |
| chablis | chablis |
| sched. | sched. |
| neighbourliness | neighbourliness |
| plainclothes | plainclothes |
| push-button | push-button |
| lux | lux |
| sturgeon | sturgeon |
| hundredweight | hundredweight |
| dept. | dept. |
| att | att |
| lungfish | lungfish |
| cyclops | cyclops |
| bonefish | bonefish |
| esq. | esq. |
| barracuda | barracuda |
| sandgrouse | sandgrouse |
| bourgeois | bourgeois |
| silverfish | silverfish |
| hermeneutics | hermeneutics |
| pince-nez | pince-nez |
| grayling | grayling |
| ptarmigan | ptarmigan |
| firstborn | firstborn |
| monkfish | monkfish |
| karateka | karateka |
| haiku | haiku |
| krill | krill |
| sprat | sprat |
| wpm | wpm |
| dogfish | dogfish |
| gal. | gal. |
| elk | elk |
| kama | kama |
| orthopaedics | orthopaedics |
| yeti | yeti |
| manga | manga |
| cwt. | cwt. |
| elevenses | elevenses |
| lionfish | lionfish |
| deni | deni |
| phlox | phlox |
| bonito | bonito |
| sapiens | sapiens |
| goby | goby |
| pomfret | pomfret |
| turbot | turbot |
| rin | rin |
| gaijin | gaijin |
| triceps | triceps |
| coloratura | coloratura |
| daimyo | daimyo |
| chon | chon |
| flatfish | flatfish |
| kanji | kanji |
| baht | baht |
| impatiens | impatiens |
| glans | glans |
| nid | nid |
| hao | hao |
| champers | champers |
| caries | caries |
| geisha | geisha |
| pilchard | pilchard |
| meatus | meatus |
| revers | revers |
| yakuza | yakuza |
| shad | shad |
| fils | fils |
| illus. | illus. |
| pers. | pers. |
| goldilocks | goldilocks |
| civics | civics |
| secs. | secs. |
| kbp | kbp |
| sai | sai |
| yellowfin | yellowfin |
| coulis | coulis |
| rd. | rd. |
| relais | relais |
| hadith | hadith |
| pris | pris |
| ber | ber |
| thrips | thrips |
| glassworks | glassworks |
| megahertz | megahertz |
| kittiwake | kittiwake |
| ibex | ibex |
| contretemps | contretemps |
| kwacha | kwacha |
| dep. | dep. |
| sunfish | sunfish |
| commis | commis |
| sifu | sifu |
| chs. | chs. |
| crossbones | crossbones |
| overindebtedness | overindebtedness |
| admin. | admin. |
| inro | inro |
| katana | katana |
| mother-goddess | mother-goddess |
| franglais | franglais |
| nones | nones |
| jomo | jomo |
| shigella | shigella |
| app. | app. |
| shortsightedness | shortsightedness |
| harees | harees |
| cantus | cantus |
| ll. | ll. |
| pleasurecraft | pleasurecraft |
| sombreness | sombreness |
| lip-gloss | lip-gloss |
| kana | kana |
| triggerfish | triggerfish |
| abies | abies |
| centredness | centredness |
| finings | finings |
| printworks | printworks |
| saccharomyces | saccharomyces |
| kes | kes |
| manus | manus |
| virginal | virginal |
| vol-au-vent | vol-au-vent |
| callisthenics | callisthenics |
| anopheles | anopheles |
| back-to-basics | back-to-basics |
| ema | ema |
| gurnard | gurnard |
| ha'p'orth | ha'p'orth |
| pas | pas |
| spec. | spec. |
| hagfish | hagfish |
| canadiens | canadiens |
| fol. | fol. |
| hautbois | hautbois |
| bento | bento |
| haemodynamics | haemodynamics |
| nishi | nishi |
| sweetlips | sweetlips |
| tesla | tesla |
| grapeshot | grapeshot |
| askari | askari |
| phragmites | phragmites |
| lat. | lat. |
| comp. | comp. |
| ccf | ccf |
| nicker | nicker |
| baren | baren |
| tonya | tonya |
| pt. | pt. |
| sensei | sensei |
| km/hr | km/hr |
| ukiyo-e | ukiyo-e |
| railworks | railworks |
| autopoiesis | autopoiesis |
| butterfish | butterfish |
| gr. | gr. |
| bata | bata |
| kilohertz | kilohertz |
| sika | sika |
| ephialtes | ephialtes |
| nosferatu | nosferatu |
| koss | koss |
| vibroseis | vibroseis |
| kaj | kaj |
| sheepe | sheepe |
| congeries | congeries |
| duergar | duergar |
| kmph | kmph |
| sawbones | sawbones |
| mele | mele |
| picosiemens | picosiemens |
| half-heartedness | half-heartedness |
| selfconsciousness | selfconsciousness |
| katakana | katakana |
| nabs | nabs |
| butterfingers | butterfingers |
| choros | choros |
| phalaris | phalaris |
| shinkansen | shinkansen |
| lithofacies | lithofacies |
| dyeworks | dyeworks |
| daddy-long-legs | daddy-long-legs |
| fusilli | fusilli |
| ringgit | ringgit |
| isu | isu |
| fibre-optics | fibre-optics |
| becak | becak |
| lefthandedness | lefthandedness |
| parados | parados |
| longlegs | longlegs |
| plateglass | plateglass |
| trans. | trans. |
| snookums | snookums |
| openmindedness | openmindedness |
| kesa | kesa |
| adm. | adm. |
| prov. | prov. |
| pantun | pantun |
| yonsei | yonsei |
| pufferfish | pufferfish |
| kami | kami |
| conatus | conatus |
| juglans | juglans |
| adj. | adj. |
| dalles | dalles |
| hawkfish | hawkfish |
| unsavouriness | unsavouriness |
| hanja | hanja |
| meta-ethics | meta-ethics |
| opticks | opticks |
| pan-pipes | pan-pipes |
| mousseux | mousseux |
| rockfish | rockfish |
| jelly-fish | jelly-fish |
| goody-two-shoes | goody-two-shoes |
| anableps | anableps |
| sidhe | sidhe |
| saltworks | saltworks |
| cres. | cres. |
| gigahertz | gigahertz |
| gov. | gov. |
| maki | maki |
| antiaircraft | antiaircraft |
| vic. | vic. |
| depts. | depts. |
| portos | portos |
| haole | haole |
| semi-works | semi-works |
| porcini | porcini |
| supp. | supp. |
| statis | statis |
| glass-works | glass-works |
| lazybones | lazybones |
| miniseries | miniseries |
| soi | soi |
| good-heartedness | good-heartedness |
| anglerfish | anglerfish |
| fairmindedness | fairmindedness |
| paedomorphosis | paedomorphosis |
| tabes | tabes |
| four-eyes | four-eyes |
| bloodymindedness | bloodymindedness |
| fo. | fo. |
| obi | obi |
| politicks | politicks |
| keris | keris |
| repr. | repr. |
| superfecundity | superfecundity |
| colocynthis | colocynthis |
| datacommunications | datacommunications |
| pickerel | pickerel |
| kapu | kapu |
| lari | lari |
| tawara | tawara |
| houmus | houmus |
| creoleness | creoleness |
| str. | str. |
| thebe | thebe |
| gallowglass | gallowglass |
| dunamis | dunamis |
| mathematicks | mathematicks |
| utis | utis |
| colour-blindness | colour-blindness |
| above-stairs | above-stairs |
| codfish | codfish |
| scheds. | scheds. |
| numbfish | numbfish |
| tournedos | tournedos |
| teddys | teddys |
| tej | tej |
| eurhythmics | eurhythmics |
| beya | beya |
| limeworks | limeworks |
| colourfulness | colourfulness |
| newes | newes |
| man. | man. |
| babykins | babykins |
| yukata | yukata |
| kango | kango |
| motorcross | motorcross |
| chem. | chem. |
| moai | moai |
| cy-pres | cy-pres |
| fols. | fols. |
| irori | irori |
| deg. | deg. |
| trumpetfish | trumpetfish |
| aua | aua |
| klar | klar |
| scorpionfish | scorpionfish |
| longshanks | longshanks |
| bejabers | bejabers |
| ser. | ser. |
| fulfilness | fulfilness |
| wendigo | wendigo |
| kakemono | kakemono |
| rec. | rec. |
| presbyacusis | presbyacusis |
| waza-ari | waza-ari |
| litotes | litotes |
| psy-ops | psy-ops |
| sweetums | sweetums |
| ali'i | ali'i |
| phosphorous | phosphorous |
| leod | leod |
| rabbitfish | rabbitfish |
| anthropometrics | anthropometrics |
| hakama | hakama |
| imp. | imp. |
| mahboob | mahboob |
| prec. | prec. |
| palagi | palagi |
| longyi | longyi |
| gnudi | gnudi |
| taonga | taonga |
| ictus | ictus |
| pondus | pondus |
| factness | factness |
| blewits | blewits |
| soapworks | soapworks |
| humourlessness | humourlessness |
| smallmindedness | smallmindedness |
| wt. | wt. |
| eerieness | eerieness |
| vigourlessness | vigourlessness |
| millihertz | millihertz |
| ghoti | ghoti |
| lampuki | lampuki |
| diplomatics | diplomatics |
| off. | off. |
| lightmindedness | lightmindedness |
| prep. | prep. |
| kermes | kermes |
| dim-wittedness | dim-wittedness |
| dim. | dim. |
| tizwas | tizwas |
| katharsis | katharsis |
| pierogi | pierogi |
| shizoku | shizoku |
| ostitis | ostitis |
| clearsightedness | clearsightedness |
| fiberoptics | fiberoptics |
| pruritis | pruritis |
| superficies | superficies |
| scrubfowl | scrubfowl |
| sobersides | sobersides |
| toadfish | toadfish |
| scup | scup |
| remora | remora |
| ductus | ductus |
| stapes | stapes |
| redfish | redfish |
| homoeostasis | homoeostasis |
| anti-aircraft | anti-aircraft |
| country-blues | country-blues |
| chermes | chermes |
| soft-heartedness | soft-heartedness |
| mithai | mithai |
| unattachedness | unattachedness |
| charr | charr |
| shiitake | shiitake |
| kaiju | kaiju |
| gtt | gtt |
| juku | juku |
| doublemindedness | doublemindedness |
| jiao | jiao |
| not. | not. |
| bn. | bn. |
| cad. | cad. |
| jiaozi | jiaozi |
| faint-heartedness | faint-heartedness |
| oecus | oecus |
| microspecies | microspecies |
| hellspawn | hellspawn |
| colourfastness | colourfastness |
| onwardness | onwardness |
| savouriness | savouriness |
| aufwuchs | aufwuchs |
| basa | basa |
| hot-headedness | hot-headedness |
| angrez | angrez |
| lapsus | lapsus |
| work-camp | work-camp |
| oleas | oleas |
| electro-magnetics | electro-magnetics |
| shetani | shetani |
| smartypants | smartypants |
| kumiss | kumiss |
| karbovanets | karbovanets |
| bk. | bk. |
| brassworks | brassworks |
| second-handedness | second-handedness |
| openheartedness | openheartedness |
| assoc. | assoc. |
| mawashi | mawashi |
Note: these words have been obtained from Wiktionary and have been classified and improved through automated computer linguistics processes.