From Longman Dictionary of Contemporary EnglishApril foolˌApril ˈfool noun [countable] TRICK/DECEIVEsomeone who is tricked on April Fools’ Day, or the trick that is played on them
Examples from the Corpus
April fool• I mentioned the review to a friend of mine who was convinced it was an April fool joke.• Just in case you don't already know, our Yobots piece was an April fool.• Commiserations to all readers who were taken in by our April fool.• Listeners were finally put out of their misery just before midday when broadcasters finally admitted to the April Fool. 