"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)).
early 15c., "to fall in flakes," from flake (n.). Related: Flaked; flaking.
A total failure; flop (1970s+)
: Don't act so flake (1960s+ Baseball)
[all except police senses ultimately fr an attested phrase snow flakes, ''cocaine'']