A blade is the flat, sharp-edged part of a tool designed for cutting. The blade of a knife slices through food, and the blade of scissors cuts paper. Even a lawnmower has blades that spin rapidly to cut grass.

Blades work because their thin, sharp edges concentrate force into a small area. When you press a knife's blade against an apple, all that pressure focuses on a tiny line, letting the blade slice through. A dull blade has a thicker, rounded edge that can't concentrate force as well, which is why sharp blades cut more easily than dull ones.

The word can also describe flat, narrow objects that resemble cutting blades in shape. A blade of grass is a single piece of grass, thin and flat like a knife blade. The blades of a fan or helicopter are the flat pieces that spin to move air. Ice skaters glide on thin metal blades attached to the bottom of their skates. A shoulder blade is the flat, triangular bone in your upper back (though it doesn't cut anything).

People sometimes use blade poetically. A bladesmith is a craftsperson who forges knives. Someone might call a skilled fencer “a master of the blade.”