early 15c., from Middle French employer, from Old French emploiier (12c.) "make use of, apply; increase; entangle; devote," from Latin implicare "enfold, involve, be connected with," from in- (see in- (2)) + plicare "to fold" (see ply (v.1)).
Sense of "hire, engage" first recorded in English 1580s, from "involve in a particular purpose," a sense which arose in Late Latin. Related: Employed; employing. The noun is 1660s, from French emploi. Imply, which is the same word, retains more of the original sense.