英语词源字典 - 在线词源网站

ass (n.2)[ass 词源字典]: slang for "backside," first attested 1860 in nautical slang, in popular use from 1930; chiefly U.S.; from dialectal variant pronunciation of arse (q.v.). The loss of -r- before -s- attested in several other words (such as burst/bust, curse/cuss, horse/hoss, barse/bass, garsh/gash). Indirect evidence of the change from arse to ass can be traced to 1785 (in euphemistic avoidance of ass "donkey" by polite speakers) and perhaps to Shakespeare, if Nick Bottom transformed into a donkey in "A Midsummer Night's Dream" (1594) is the word-play some think it is. Meaning "woman regarded as a sexual object" is from 1942. To have (one's) head up (one's) ass "not know what one is doing" is attested by 1969. Colloquial (one's) ass "one's self, one's person" attested by 1958.[ass etymology, ass origin, 英语词源]
couch (v.): c. 1300, "to overlay with gold, inlay," from Old French couchier "to lay down, place; go to bed, put to bed," from Latin collocare "to lay, place, station, arrange," from com- "together" (see com-) + locare "to place" (see locate). Meaning "to put into words" is from 1520s. Related: Couched; couching. Heraldic couchant ("lying down with the head up") is late 15c., from the French present participle.
head (v.): "to be at the head or in the lead," c. 1200, from head (n.). Meaning "to direct the head (toward)" is from c. 1600. Related: headed, heading. The earliest use of the word as a verb meant "behead" (Old English heafdian). Verbal phrase head up "supervise, direct" is attested by 1930.