fagyoudaoicibaDictYouDict[fag 词源字典]
fag: English has three distinct words fag, none of whose origins is altogether clear. The oldest is the one which denotes ‘drudgery’. It is first recorded as a verb in the 16th century, meaning ‘droop, decline’; its more common noun uses, ‘hard boring work’ and ‘boy who does tasks for an older boy in a British public school’, appear to have developed in the late 18th century.

It is generally taken to have been originally an alteration of flag ‘lose vigour, droop’, although there is no conclusive proof of this. Fag ‘cigarette’ [19] is an abbreviation of fag-end [17], which originally meant generally ‘extreme end’. It was a compound formed from an earlier fag [15], whose underlying meaning seems to have been something like ‘piece hanging down loosely, flap’ (and which conceivably could be related to fag ‘drudgery’). Fag ‘homosexual’ [20] is short for faggot [13], a derogatory term applied to male homosexuals in American English since the early 20th century; the usage is probably based on the slightly earlier uncomplimentary use of the word for ‘woman’. Faggot means literally ‘bundle of sticks’, and comes via Old French fagot from Italian faggotto (which is used also for ‘bassoon’).

This in turn is a diminutive form of Vulgar Latin *facus, which was based ultimately on Greek phákelos ‘bundle’. The notion of applying a term for ‘bundle’ abusively to ‘women’ is perhaps echoed in baggage.

[fag etymology, fag origin, 英语词源]
fag (v.1)youdaoicibaDictYouDict
"to droop, decline in strength, become weary" (intransitive), 1520s, of uncertain origin; OED is content with the "common view" that it is an alteration of flag (v.) in its sense of "droop, go limp." Transitive sense of "to make (someone or something) fatigued, tire by labor" is first attested 1826. Related: Fagged; fagging.
fag (n.1)youdaoicibaDictYouDict
British slang for "cigarette" (originally, especially, the butt of a smoked cigarette), 1888, probably from fag "loose piece, last remnant of cloth" (late 14c., as in fag-end "extreme end, loose piece," 1610s), which perhaps is related to fag (v.), which could make it a variant of flag (v.).
fag (v.2)youdaoicibaDictYouDict
"put to work at certain duties, compel to work for one's benefit," 1806, from British public school slang fag (n.) "junior student who does certain duties for a senior" (1785), from fag (v.1). Related: Fagdom (1902); faggery "fatiguing labor" (1853).
fag (n.2)youdaoicibaDictYouDict
shortening of faggot (n.2) "male homosexual," by 1921. Fag hag "heterosexual woman who keeps company with gay men" attested by 1969.