yes (adv.) Look up yes at Dictionary.com
Old English gise, gese "so be it!," probably from gea, ge "so" (see yea) + si "be it!," third person imperative of beon "to be" (see be). Originally stronger than simple yea. Used in Shakespeare mainly as an answer to negative questions. As a noun from 1712. Yes-man is first recorded 1912, American English.