chaps (n.1)

1844, American English, short for chaparejos, from Mexican Spanish chaparreras, leather overalls worn to protect riders' legs from the chaparro (see chaparral).

"jaws, cheeks," from chap (n.), 1550s, which is of unknown origin. Hence, chap-fallen "with the lower jaw hanging down" (1590s), hence, figuratively, "dejected, disspirited" (c. 1600).