feast (v.) Look up feast at Dictionary.com
c.1300, "partake of a feast," from Old French fester "to feast, make merry; observe (a holiday)" (Modern French fêter), from feste "religious festival" (see feast (n.)). Related: Feasted; feasting.
feast (n.) Look up feast at Dictionary.com
c.1200, "secular celebration with feasting and entertainment" (often held on a church holiday); c.1300, "religious anniversary characterized by rejoicing" (rather than fasting), from Old French feste "religious festival, holy day; holiday; market, fair; noise, racket; jest, fun" (12c., Modern French fête), from Vulgar Latin *festa (fem. singular; also source of Italian festa, Spanish fiesta), from Latin festa "holidays, feasts, festal banquets," noun use of neuter plural of festus "festive, joyful, merry," related to feriae "holiday" and fanum "temple," from Proto-Italic *fasno- "temple," from PIE *dhis-no- "divine, holy; consecrated place," from *dhes- "root of words in religious concepts" [Watkins].

The spelling -ea- was used in Middle English to represent the sound we mis-call "long e." Meaning "abundant meal" (whether public or private) is by late 14c. Meaning "any enjoyable occasion or event" is from late 14c.