April Fool: One who is tricked by others into believing or doing something on the first day of April.

Fool: One who is regarded as deficient in judgment, sense or understanding.

One who acts unwisely on a given occasion.
One who has been tricked or made to appear ridiculous; a dupe.
Informal: A person with a talent or an enthusiasm for a certain activity: a
dancing fool; a fool for skiing.
A member of a royal or noble household who provided entertainment, as with jokes or antics; a jester.
A dessert made of stewed or purйed fruit mixed with cream or custard and
served cold.
Archaic: A mentally deficient person; an idiot.

Fool's Cap: A cap with bells attached worn by jesters.

Fool's Errand: A silly, profitless task.

Fool's Gold: Gold colored iron or copper pyrites, often mistaken for gold.

Fool's Paradise: A make-believe place of vanity and nonsense.

Fool's Parsley: An annual plant that resembles parsley, but nauseous and poisonous.

Playing the Fool: To act like the idiot or foolishly.

Tomfoolery: The act of foolishness or silliness.

Trompe l'oeil: An artistic term meaning "fool the eye". A painting that simulates 3-dimensions or marble is Trompe l'oeil. There are incredible examples in the Vatican.