(idiomatic) A foolish undertaking, especially one that is purposeless, fruitless, nonsensical, or certain to fail. / (idiomatic) Such an undertaking, assigned as a prank.

present participle of fool about

(intransitive) to fool around

(intransitive) to play the fool

(idiomatic) To behave in a foolish or comical manner. / (idiomatic) To pretend/feign ignorance.

(archaic, intransitive) To act foolishly.

(colloquial, transitive) to trick/fool somebody

Aethusa cynapium, an annual umbelliferous plant that resembles parsley but is poisonous.

Having the heart of a fool; foolish.

(set phrase) A person who is not easily deceived or victimized; one who is perceptive, clever, or thoroughly common-sensical.