April borrows three days of March, and they are ill.

The proverb imagines April taking three days from March to explain why part of April can feel disagreeable. The borrowed days retain the character of the earlier month.

It conveys the idea that turning a calendar page does not necessarily bring an immediate change in conditions. Unpleasant days may linger into a month expected to feel different.

Use it to comment on a spell of unpleasant weather in April that feels more like March. The borrowing is a figurative way to describe the persistence of those conditions, not a claim about particular calendar dates.