fair (adj.) Look up fair at Dictionary.com
Old English fæger "beautiful, lovely, pleasant," from Proto-Germanic *fagraz (cognates: Old Saxon fagar, Old Norse fagr, Old High German fagar "beautiful," Gothic fagrs "fit"), perhaps from PIE *pek- (1) "to make pretty" (cognates: Lithuanian puošiu "I decorate").

The meaning in reference to weather (c.1200) preserves the original sense (opposed to foul). Sense of "light-complexioned" (1550s) reflects tastes in beauty; sense of "free from bias" (mid-14c.) evolved from another early meaning, "morally pure, unblemished" (late 12c.). The sporting senses (fair ball, fair catch etc.) began in 1856. Fair play is from 1590s; fair and square is from c.1600. Fair-haired in the figurative sense of "darling, favorite" is from 1909. First record of fair-weather friends is from 1736.
fair (n.) Look up fair at Dictionary.com
early 14c., from Anglo-French feyre (late 13c.), from Old French feire, from Vulgar Latin *feria "holiday, market fair," from Latin feriae "religious festivals, holidays," related to festus "solemn, festive, joyous" (see feast).