funyoudaoicibaDictYouDict[fun 词源字典]
fun: [17] A fun was originally a ‘trick, hoax, practical joke’: ‘A Hackney Coachman he did hug her, and was not this a very good Fun?’ Thomas D’Urfey, Pills to Purge Melancholy 1719. It came from the contemporary verb fun ‘cheat, hoax’, which was presumably a variant of the Middle English verb fon ‘make a fool of’. This in turn was a verbal use of the noun fon ‘fool’, probable origin of modern English fond.

The current sense of fun, ‘amusement, merriment’, did not develop until the 18th century. The derived adjective funny, in the sense ‘amusing’, was roughly contemporary with it; ‘strange, odd’ is an early 19th-century semantic development.
=> fond[fun etymology, fun origin, 英语词源]
fun (n.)youdaoicibaDictYouDict
"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 1906.
fun (v.)youdaoicibaDictYouDict
1680s, "to cheat;" 1833 "to make fun, jest, joke," from fun (n.). Related: Funning.
fun (adj.)youdaoicibaDictYouDict
mid-15c., "foolish, silly;" 1846, "enjoyable," from fun (n.).