chaps (n.1) Look up chaps at Dictionary.com
1844, American English, short for chaparejos, from Mexican Spanish chaparreras, overalls worn to protect from chaparro (see chaparral).
chaps (n.2) Look up chaps at Dictionary.com
"jaws, cheeks," from chap (n.), 1550s, of unknown origin. Hence, chap-fallen (1590s).