Americans seem to have a preoccupation with "fun." However, the word has a checkered history, etymologically speaking.
As noted by Douglas Harper, its earliest uses are bound up with notions of trickery.
"fun (n.) ...'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...). 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' [designating] 'counterfeit bills' (1938, though this use of the word may be more for the sake of the rhyme). ...1680s, 'to cheat' ...mid-15c., 'foolish, silly' ..."
Of course, the Tarot trumps begin with the Fool - emblazoned with the 0. About the word, Aleister Crowley noted: "...'Fool' is derived from 'follis,' a wind-bag."
For information on the veiled meaning of the phrase "Sow Your Wild Oats," see "Sometimes, Sayings Say More than The Sayer Wants Said.".
 Master Therion [Aleister Crowley], The Book of Thoth, reprint ed., Stamford, Ct.: U.S. Games Sys., Inc., 1996, p. 53.