Aˈpril-fish noun

An April fool's hoax, deception or errand (translation of Fr poisson d'avril)

April fool noun

1. A person who is hoaxed, deceived, or made a fool of on 1 April (in Scotland also called a gowk, as in the phrase hunt-the-gowk (qv))
2. A hoax or trick played on that day

April Fools' Day noun

1 April, the day on which tricks are traditionally played and fools made