In Poland, what Latin phrase names April Fools' Day?

In Poland, the Latin phrase for April Fools’ Day is prima Aprilis.

The expression literally means “the first of April” and names Poland’s traditional day for pranks, hoaxes and playful deception. The custom is centuries old, and Polish people may use elaborate false stories rather than only small practical jokes.

April 1 is treated with unusual suspicion in Poland: serious statements may be doubted, and media outlets or public institutions sometimes cooperate in making a hoax sound credible. A historical example of this caution concerns Poland’s anti-Turkish alliance with Leopold I, signed on April 1, 1683; the date was reportedly changed to March 31 because the original date seemed unbelievable.

Prima Aprilis is not the same as the Feast of Fools, a medieval festival sometimes mentioned as a possible related tradition. Nor is it the Polish name for a general New Year celebration. In some Polish communities, jokes are traditionally considered acceptable only until noon, after which continuing them may be viewed as poor form.