bumyoudaoicibaDictYouDict[bum 词源字典]
bum: There are two distinct words bum in English. By far the older, ‘buttocks’, is first recorded in John de Trevisa’s translation of Ranulph Higden’s Polychronicon 1387: ‘It seemeth that his bum is out that hath that evil [piles]’. It is not clear where it comes from. The other, ‘tramp, loafer’, and its associated verb ‘spend time aimlessly’ [19], chiefly American, probably come from an earlier bummer, derived from the German verb bummeln ‘loaf around, saunter’ (familiar to English speakers from the title of Jerome K Jerome’s novel Three Men on the Bummel 1900, about a jaunt around Germany).
[bum etymology, bum origin, 英语词源]
gallivant (v.)youdaoicibaDictYouDict
"gad about, spend time in frivolous pleasure-seeking, especially with the opposite sex," 1809, of uncertain origin, perhaps a playful elaboration of gallant in an obsolete verbal sense of "play the gallant, flirt, gad about." Related: Gallivanted; gallivanting.
Young Lobski said to his ugly wife,
"I'm off till to-morrow to fish, my life;"
Says Mrs. Lobski, "I'm sure you a'nt",
But you brute you are going to gallivant."

What Mrs. Lobski said was right,
Gay Mr. Lobski was out all night.
He ne'er went to fish, 'tis known very well
But where he went I shall not tell.

["Songs from the Exile," in "Literary Panorama," London, 1809]
hang (v.)youdaoicibaDictYouDict
a fusion of Old English hon "suspend" (transitive, class VII strong verb; past tense heng, past participle hangen), and Old English hangian "be suspended" (intransitive, weak, past tense hangode); also probably influenced by Old Norse hengja "suspend," and hanga "be suspended." All from Proto-Germanic *hanhan (transitive), *hangen (intransitive) "to hang" (cognates: Old Frisian hangia, Dutch hangen, German hängen), from PIE *konk- "to hang" (cognates: Gothic hahan, Hittite gang- "to hang," Sanskrit sankate "wavers," Latin cunctari "to delay;" see also second element in Stonehenge).

As a method of execution, in late Old English (but originally specifically of crucifixion). Meaning "to come to a standstill" (especially in hung jury) is from 1848, American English. Hung emerged as past participle 16c. in northern England dialect, and hanged endured only in legal language (which tends to be conservative) in reference to capital punishment and in metaphors extended from it (I'll be hanged).

Teen slang sense of "spend time" first recorded 1951; hang around "idle, loiter" is from 1828, American English; also compare hang out. To hang back "be reluctant to proceed" is from 1580s; phrase hang an arse "hesitate, hold back" is from 1590s. Verbal phrase hang fire (1781) originally was used of guns that were slow in communicating the fire through the vent to the charge. To let it all hang out "be relaxed and uninhibited" is from 1967.
faffyoudaoicibaDictYouDict
"Spend time in ineffectual activity", Late 18th century (originally dialect in the sense 'blow in puffs', describing the wind): imitative. The current sense may have been influenced by dialect faffle 'stammer, stutter', later 'flap in the wind', which came to mean 'fuss, dither' at about the same time as faff (late 19th century). More Originally a dialect word for ‘blow in puffs or small gusts’, faff was describing the wind, imitating the sound. The current sense may have been influenced by dialect faffle initially meaning ‘stammer, stutter’, later ‘flap in the wind’, which came to mean ‘fuss or dither’ at about the same time as faff in the late 19th century.