A roller is a cylinder-shaped object that spins or rolls, used for many different purposes depending on its size and what it's made of.

Paint rollers have soft, absorbent covers that soak up paint and spread it smoothly across walls, much faster than a brush could. Road rollers are massive machines with huge steel cylinders that press down on fresh asphalt to make it flat and solid. Bakers' rolling pins are wooden rollers that flatten dough for cookies and pies.

Rollers work because of their shape: as they turn, they touch a surface along their entire length at once, spreading pressure or material evenly. Hair rollers curl hair by wrapping it around their cylindrical shape. Conveyor belt rollers spin underneath to keep packages moving smoothly through warehouses.

The word also describes certain types of waves that roll steadily toward shore, one after another, or a kind of canary bred for its long, rolling song.

When something moves smoothly forward like a turning cylinder, we say it's rolling, whether it's a ball, a wheelchair, or even your eyes when you're exasperated.