flatter.

Inherited from 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”), *flataz (“flat”), from Proto-Indo-European *plÁt-, *pele-, *plet-, *plāk- (“flat, broad, plain”). Cognate with Old High German flazza (“palm, flat of the hand”), Old High German flaz (“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, flétrir.