"thin, flat piece," early 14c., possibly from Old English *flacca "flakes of snow," from Old Norse flak "loose or torn piece" (related to Old Norse fla "to skin," see flay), from Proto-Germanic *flago- (cf. Middle Dutch vlac, Dutch vlak "flat, level," Middle High German vlach, German Flocke "flake"); from PIE *plak- (1) "to be flat," extended form of root *pele- (2) "flat, to spread" (see plane (n.1)).