Fish is Old English fisc, and the sh spelling is the tidy modern outcome of that sc. Old English wrote the sound sc; modern English writes it sh, in ship, shall, shape and fish. This matters for spotting Norse borrowings, because Norse did not soften its sc- the way English did — so where English has sh, Norse-derived words kept sk, giving the pairs shirt and skirt, shatter and scatter.
The word may go back to an Indo-European root for fish, though one scholar argues on phonetic grounds that it was borrowed into Germanic from some older language of northwestern Europe. English has always used it loosely for anything living entirely in water, which is why shellfish and starfish are called fish despite being nothing of the kind. The plural behaves in the old Germanic way: fishes when counting kinds, fish when treating them as a mass.
fish (n.) "a vertebrate which has gills and fins adapting it for living in the water," Old English fisc "fish," from Proto-Germanic *fiskaz (source also of Old Saxon, Old Frisian, Old High German fisc , Old Norse fiskr , Middle Dutch visc , Dutch vis , German Fisch , Gothic fisks ), perhaps from PIE root *pisk- "a fish." But Boutkan on phonetic grounds thinks it might be a northwestern Europe substratum word. Popularly, since Old English, "any animal that lives entirely in the water," hence shellfish , starfish (an early 15c. manuscript has fishes bestiales for "water animals other than fishes"). The plural is fishes , but in a collective sense, or in reference to fish meat as food, the singular fish generally serves for a plural. In reference to the constellation Pisces from late 14c. Fish (n.) for "person" is from 1750 with a faintly dismissive sense; earlier it was used in reference to a person considered desirable to "catch" (1722). Figurative sense of fish out of water "person in an unfamiliar and awkward situation" attested by 1610s ( a fisshe out of the see in the same sense is from mid-15c.). To drink like a fish is from 1744. To have other fish to fry "other objects which invite or require attention" is from 1650s. Fish-eye as a type of lens is from 1961. Fish-and-chips is from 1876; fish-fingers from 1962. fish (v.) Old English fiscian "to fish, to catch or try to catch fish" (cognates: Old Norse fiska , Old High German fiscon , German fischen , Gothic fiskon ), from the root of fish (n.). Related: Fished ; fishing .
fish came in through Old English, and its spelling follows that family's conventions.
How that family writes these sounds
| /f/ | f, the plain letter — never phfish, fire, wolf |
What gives it away on the page
| sh | The regular modern shape of Old English sc-.ship, fish, shall |
Old English in the spelling guide · guess another word's family