Yours, Etc.: Origins and Uses of 8 Sign-Offs
French private soldier, 1914, from French poilu, literally "hairy," from poil "hair," not of the head, but of beards, animal coats, etc., from Latin pilus (see pile (n.3)). In 19c. French the adjective had a secondary sense of "strong, brave, courageous" (Balzac).