A slit is a long, narrow opening or cut. Picture the slot where you drop coins into a piggy bank, or the thin gap in a mailbox where letters slide through: those are slits. Venetian blinds have slits between them that let you control how much light enters a room.

When used as a verb, to slit means to make such a cut, usually thin and precise. A baker might slit the top of bread dough before baking to help it rise evenly. Someone might carefully slit open an envelope with a letter opener instead of tearing it messily.

Slits appear throughout nature and design because they're useful. Castle walls had slits called arrow loops where archers could shoot outward while staying protected. Some snakes and cats have vertical slits for pupils, which help them see well in varying light conditions. The word captures that specific kind of opening: not a hole, not a gash, but a clean, narrow gap that serves a purpose.