Noun

1. A person subjected to a practical joke on April Fools' Day. Often used as an exclamation upon revealing the joke.
   • 1785, Francis Grose, A Classical Dictionary of the Vulgar Tongue, p 4:

     APRIL FOOL, Any one imposed on, or sent on a bootless errand on the first of April, on which day it is the custom among the lower people, children, and servants, by dropping empty papers carefully doubled up, sending persons on absurd messages, and such like contrivances, to impose on every one they can, and then to salute them with the title of April-fool.

2. A practical joke played on April Fools' Day.