something that provides mirth or amusement

A picnic would be fun.

enjoyment or playfulness

She's full of fun.

Informal . joke; kid.

Informal . of or pertaining to fun, esp. to social fun

a fun thing to do; really a fun person.

Informal . whimsical: flamboyant

The fashions this year are definitely on the fun side.

for or in fun

as a joke; not seriously; playfully

His insults were only in fun.

like fun

Informal . certainly not; of doubtful truth

He told us that he finished the exam in an hour. Like fun he did!

make fun of

to make the object of ridicule; deride

The youngsters made fun of their teacher.