"tuft of hair behind the pastern-joint of a horse," early 14c., fetlak, from a Germanic source (cognates: Dutch vetlock, Middle High German fizlach, German Fiszloch), perhaps from Proto-Germanic *fetel- (source of German fessel "pastern"), from PIE *ped-el-, from root *ped- (1) "foot" (see foot (n.)). The Middle English diminutive suffix -ok (from Old English -oc) was misread and the word taken in folk etymology as a compound of feet and lock (of hair).
