n.
 light-hearted pleasure or amusement. 
▸a source of fun:
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 people-watching is great fun.
▸playfulness or good humour:
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 she's full of fun.
adj.
 informal entertaining or enjoyable.
v.
 (funs, funning, funned)
 N. Amer. informal joke or tease.
Phrase
  
    - in fun
 not intended seriously.
- make fun of
 tease or laugh at in a mocking or unkind way.
 
  Etymology
  C17 (denoting a trick or hoax): from obs. fun ‘to cheat or hoax’, dial. var. of ME fon ‘make a fool of, be a fool’, rel. to fon ‘a fool’, of unknown origin; cf. fond.