wagyoudaoicibaDictYouDict[wag 词源字典]
wag: [13] Wag was derived from the Middle English descendant of Old English wagian ‘totter’, a word related to English wave of the sea. Waggle [15] was based on it. The noun wag ‘comical fellow’, first recorded in the 16th century, is generally taken to be short for waghalter, literally ‘someone who swings to and fro in a noose’, hence ‘someone destined for the gallows’.
=> waggle[wag etymology, wag origin, 英语词源]
wag (v.)youdaoicibaDictYouDict
early 13c. (intransitive), "waver, vacillate, lack steadfastness," probably from a Scandinavian source (compare Old Norse vagga "a cradle," Danish vugge "rock a cradle," Old Swedish wagga "fluctuate, rock" a cradle), and in part from Old English wagian "move backwards and forwards;" all from Proto-Germanic *wag- (cognates: Old High German weggen, Gothic wagjan "to wag"), probably from PIE root *wegh- "to move about" (see weigh).

Transitive meaning "move (something) back and forth or up and down" is from c. 1300; of dogs and their tails from mid-15c.: "and whanne they [hounds] see the hure maystre they wol make him cheere and wagge hur tayles upon him." [Edward, Duke of York, "The Master of Game," 1456]. Related: Wagged; wagging. Wag-at-the-wall (1825) was an old name for a hanging clock with pendulum and weights exposed.
wag (n.1)youdaoicibaDictYouDict
"person fond of making jokes," 1550s, perhaps a shortening of waghalter "gallows bird," person destined to swing in a noose or halter, applied humorously to mischievous children, from wag (v.) + halter. Or possibly directly from wag (v.); compare wagger "one who stirs up or agitates" (late 14c.).
wag (n.2)youdaoicibaDictYouDict
"act of wagging," 1580s, from wag (v.).