fishwife (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.

Middle English wif, wyf, from Old English wif (neuter) "woman, female, lady," also, but not especially, "wife," from Proto-Germanic *wīfa- (source also of Old Saxon, Old Frisian wif, Old Norse vif, Danish and Swedish viv, Middle Dutch, Dutch wijf, Old High German wib, German Weib), of uncertain origin and disputed etymology, not found in Gothic.

Apparently felt as inadequate in its basic sense, leading to the more distinctive formation wifman (source of woman). Dutch wijf now means, in slang, "girl, babe," having softened somewhat from earlier sense of "bitch." The Modern German cognate (Weib) also tends to be slighting or derogatory; Middle High German wip in early medieval times was "woman, female person," vrouwe (Frau) being retained for "woman of gentle birth, lady;" but from c. 1200 wip "took on a common, almost vulgar tone that restricted its usage in certain circles" and largely has been displaced by Frau.

The more usual Indo-European word is represented in English by queen/quean. Words for "woman" also double for "wife" in some languages. Some proposed PIE roots for wife include *weip- "to twist, turn, wrap," perhaps with sense of "veiled person" (see vibrate); and more recently *ghwibh-, a proposed root meaning "shame," also "pudenda," but the only examples of it would be the Germanic words and Tocharian (a lost IE language of central Asia) kwipe, kip "female pudenda."

The modern sense of "female spouse" began as a specialized sense in Old English; the general sense of "woman" is preserved in midwife, old wives' tale, etc. Middle English sense of "mistress of a household" survives in housewife; and the later restricted sense of "tradeswoman of humble rank" in fishwife. By 1883 as "passive partner in a homosexual couple." Wife-swapping is attested from 1954.