fish (n.) Look up fish at Dictionary.com
Old English fisc "fish," from Proto-Germanic *fiskaz (cognates: Old Saxon, Old Frisian, Old High German fisc, Old Norse fiskr, Middle Dutch visc, Dutch vis, German Fisch, Gothic fisks), from PIE *peisk- "fish" (cognates: Latin piscis, Irish iasc, and, via Latin, Italian pesce, French poisson, Spanish pez, Welsh pysgodyn, Breton pesk).

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 in the faintly dismissive sense; earlier it was used in reference to a person considered desirable to 'catch' (1722). Figurative sense of fish out of water first recorded 1610s. 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-story attested from 1819, from the tendency to exaggerate the size of the catch (or the one that got away). Fish-eye as a type of lens is from 1961. Fish-and-chips is from 1876; fish-fingers from 1962. Fish-food is from 1936 as "food for (pet or hobby) fish."
fish (v.) Look up fish at Dictionary.com
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.