Source : Webster's Revised Unabridged Dictionary (1913)

Fun \Fun\, n. [Perh. of Celtic origin; cf. Ir. & Gael. fonn
   pleasure.]
   Sport; merriment; frolicsome amusement. ``Oddity, frolic, and
   fun.'' --Goldsmith.

   {To make fan of}, to hold up to, or turn into, ridicule.

Source : WordNet®

fun
     adj : providing enjoyment; pleasantly entertaining; "an amusing
           speaker"; "a diverting story"; "a fun thing to do"
           [syn: {amusing}, {amusive}, {diverting}, {fun(a)}]
     [also: {funning}, {funned}]

fun
     n 1: activities that are enjoyable or amusing; "I do it for the
          fun of it"; "he is fun to have around" [syn: {merriment},
           {playfulness}]
     2: verbal wit (often at another's expense but not to be taken
        seriously); "he became a figure of fun" [syn: {play}, {sport}]
     3: violent and excited activity; "she asked for money and then
        the fun began"; "they began to fight like fun"
     4: a disposition to find (or make) causes for amusement; "her
        playfulness surprised me"; "he was fun to be with" [syn: {playfulness}]
     [also: {funning}, {funned}]

Source : Free On-Line Dictionary of Computing

Fun
     
        A {typed lambda-calculus}, similar to {SOL}[2].  "On
        Understanding Types, Data Abstractions and Polymorphism",
        L. Cardelli et al, ACM Comp Surveys 17(4) (Dec 1985).