*From Middle English flatteren, flateren (“to flutter, float, fawn over”), probably a conflation of Old English floterian, flotorian (“to flutter, float, be disquieted”), from Proto-West Germanic *flotrōn, from Proto-Germanic *flutrōną (“to be floating”), from Proto-Indo-European *plewd- (“to flow, swim”), equivalent to float + -er; and Old Norse flaðra (“to fawn on someone, flatter”), from Proto-Germanic *flaþrōną (“to fawn over, flutter”), from Proto-Indo-European *peled- (“moisture, wetness”), *pel- (“to gush, pour out, fill, flow, swim, fly”). Cognate with Scots flatter, flotter (“to float; splash; cover with liquid”), Middle Dutch flatteren (“to embellish, flatter, caress”), German flattern (“to flutter”). *The word was also falsely associated with Middle French flatter (“to flatter, to caress with the flat of the hand”), from Old French flater (“to deceive by concealing the truth, to stroke with the palm of the hand”), from Frankish *flat (“palm, flat of the hand”), from Proto-Germanic *flatą, *flatō (“palm, sole”), from *flataz (“flat”), probably from Proto-Indo-European *pleth₂-, *pleh₂- (“flat, broad, plain”); related to Old High German flazza (“palm, flat of the hand”), Old High German flaȥ (“level, flat”), Old Saxon flat (“flat”), Old Norse flatr (“flat”) (whence English flat), Old Frisian flet, flette (“dwelling, house”), Old English flet, flett (“ground floor, dwelling”). More at flat.

butter up • lay it on thick • puff • stroke someone's ego • blandander • blandish • brush up to • collogue • extol • flatterize • glaver • glaze • gloze • gratify • jolly • make fair weather • palaver • please • preen • soothe • speak well of • stroke • tickle the ear