a silly or stupid person; a person who lacks judgment or sense.

a professional jester, formerly kept by a person of royal or noble rank for amusement

the court fool.

a person who has been tricked or deceived into appearing or acting silly or stupid

to make a fool of someone.

an ardent enthusiast who cannot resist an opportunity to indulge an enthusiasm (usually prec. by a present participle)

He's just a dancing fool.

a weak-minded or idiotic person.

to trick, deceive, or impose on

They tried to fool him.

to act like a fool; joke; play.

to jest; pretend; make believe

I was only fooling.

fool around,

to putter aimlessly; waste time

She fooled around all through school.

to philander or flirt.

to be sexually promiscuous, esp. to engage in adultery.

fool away, to spend foolishly, as time or money; squander

to fool away the entire afternoon.

fool with, to handle or play with idly or carelessly

to be hurt while fooling with a loaded gun; to fool with someone's affections.

be nobody's fool

to be wise or shrewd.