A chain saw is a powerful cutting tool with a motor that spins a chain of sharp metal teeth around a flat blade. The teeth move so fast they can slice through thick tree trunks in minutes, a job that would take hours with a hand saw.

Chain saws revolutionized forestry and construction work when they became practical in the 1920s. Before chain saws, loggers spent days cutting down large trees with axes and two-person hand saws. Today, professional loggers use chain saws to harvest timber, while homeowners use smaller versions to trim branches or cut firewood.

The tool is also spelled as one word, chainsaw. Despite their usefulness, chain saws are dangerous and require serious safety training. The spinning chain moves at tremendous speed, and the saw can kick back unexpectedly if it hits at certain angles. Most places require adults to supervise any chain saw use, and professionals wear protective gear including helmets, gloves, and special chaps that can stop the chain if it touches their legs.

You might hear someone say they're going to chain saw some fallen branches, using the tool's name as a verb.