also moult, c. 1400, mouten, of feathers, hair, etc., "to be shed, fall out," from Old English *mutian "to change" (in bemutian "to exchange"), from Latin mutare "to change" (from PIE root *mei- (1) "to change"). Transitive sense, "to shed or cast (feathers, fur, skin)" is by mid-15c. With unetymological -l-, late 16c., on model of fault, etc. Related: Molted, moulted; molting, moulting. As a noun, "act or process of shedding an outer structure or appendage," from 1815.