The Collaborative International Dictionary
All Fools' Day
All Fools' Day \All" Fools' Day`\ The first day of April, a day on which sportive impositions are practiced.
The first of April, some do say,
Is set apart for All Fools' Day.
--Poor Robin's
Almanack
(1760).
Usage examples of "all fools' day".
In the darkest part of the night, on the very cusp of All Fools' Day, a tremendous crash reverberated through the Hayholt.
It was shortly after daybreak the next morning, April 1, All Fools' Day, when Adams, his son, and servant took leave of Captain Tucker and were rowed ashore.