A furrow is a long, narrow groove or trench dug into the ground, usually in a straight line. Farmers plow furrows into their fields to plant seeds in neat rows. Each furrow creates a small channel where seeds can be placed at the right depth and spacing. When you look at a freshly plowed field, those parallel lines running across it are furrows.

The word also describes similar grooves in other surfaces. When someone concentrates hard or worries deeply, they might furrow their brow, creating temporary lines across their forehead as they scrunch their face. You might notice these wrinkles on a teacher's face when she's thinking through a difficult problem, or on a friend's forehead when they're puzzled by something.

To furrow something means to make these grooves or lines. A wagon wheel can furrow a dirt road over time, cutting deeper tracks with each pass. Ocean waves can furrow the sand. The word suggests something being carved or pressed into a surface, leaving visible marks behind.