Your brow is your forehead, the smooth part of your face above your eyebrows and below your hairline. When you're concentrating hard on a difficult math problem, you might furrow your brow, creating wrinkles across it. When you're surprised, you might raise your brow.

The word also refers to the ridge of bone and hair above each eye: your eyebrow. An actor might arch a single brow to show skepticism or confusion. People express countless emotions through their brows without saying a word.

Brow can also mean the edge or top of something steep. The brow of a hill is its upper edge or crest, where you can see the land dropping away on the other side.

When someone knits their brow, they're drawing their eyebrows together in concentration or concern. To do something by the sweat of your brow means to work hard physically to accomplish it, since people sweat on their foreheads when laboring in the sun.