Etymology
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wag (v.)
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- (source also of Old High German weggen, Gothic wagjan "to wag"), probably from PIE root *wegh- "to go, move, transport in a vehicle."

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.
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wag (n.1)
"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.).
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wag (n.2)
"act of wagging," 1580s, from wag (v.).
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waggle (v.)
late 15c. (implied in waggling), frequentative of wag (v.). Compare Dutch waggelen "to waggle," Old High German wagon "to move, shake," German wackeln "to totter." Transitive sense from 1590s. Related: Waggled.
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waggish (adj.)
"willing to make a fool of oneself, and fond of doing so to others," 1580s, from wag (n.) + -ish. Related: Waggishly; waggishness.
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wagtail (n.)

c. 1500, kind of small bird that has its tail in continuous motion (late 12c. as a surname), earlier wagstart (mid-15c.), from wag (v.) + tail (n.). From 18c. as "a harlot," but this sense seems to be implied much earlier:

If therefore thou make not thy mistress a goldfinch, thou mayst chance to find her a wagtaile. [Lyly, "Midas," 1592]
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blather (v.)
1520s, blether, Scottish, probably from a Scandinavian source such as Old Norse blaðra "mutter, wag the tongue," perhaps of imitative origin, or from Proto-Germanic *blodram "something inflated" (the source of bladder). Related: Blathered; blathering.
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wheedle (v.)
"to influence by flattery," 1660s, of uncertain origin, perhaps connected with Old English wædlian "to beg," from wædl "poverty" [OED], or borrowed by English soldiers in the Thirty Years' War from German wedeln "wag the tail," hence "fawn, flatter" (compare adulation). Related: Wheedled; wheedling.
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whisk (v.)
late 15c., "move with a rapid sweeping motion" (intransitive), from a Scandinavian source (compare Danish viske "to wipe, rub, sponge," Norwegian, Swedish viska "wipe," also "wag the tail"), from the source of whisk (n.). Transitive sense is from 1510s; meaning "to brush or sweep (something) lightly over a surface" is from 1620s. Related: Whisked; whisking.
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adulation (n.)

"servile or insincere praise," late 14c., from Old French adulacion, from Latin adulationem (nominative adulatio) "a fawning; flattery, cringing courtesy," noun of action from past-participle stem of adulari "to flatter, fawn upon."

This is usually said to be from ad "to" (see ad-) + a stem meaning "tail," from a PIE *ul- "the tail" (source also of Sanskrit valah "tail-hair," and Lithuanian valai "horse's tail"). The original notion would be "to wag the tail" like a fawning dog (compare Greek sainein "to wag the tail," also "to flatter;" also see wheedle).

But de Vaan finds phonetic problems with these and concludes the etymology is uncertain, though he proposes a connection with avidus "eager," via *adulo- "who is eager toward something," hence "a flatterer." Adulation may proceed from true blind worship or be insincere, from hope of advantage.

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