fun (n.) Look up fun at Dictionary.com
"diversion, amusement, mirthful sport," 1727, earlier "a cheat, trick" (c.1700), from verb fun (1680s) "to cheat, hoax," which is of uncertain origin, probably a variant of Middle English fonnen "befool" (c.1400; see fond). Scantly recorded in 18c. and stigmatized by Johnson as "a low cant word." Older senses are preserved in phrase to make fun of (1737) and funny money "counterfeit bills" (1938, though this use of the word may be more for the sake of the rhyme). See also funny. Fun and games "mirthful carryings-on" is from 1920.
fun (v.) Look up fun at Dictionary.com
1680s, "to cheat;" 1833 "to make fun, jest, joke," from fun (n.). Related: Funning.
fun (adj.) Look up fun at Dictionary.com
mid-15c., "foolish, silly;" 1846, "enjoyable," from fun (n.).