A chainsaw is a power tool that can quickly cut through tree trunks and branches. If a tree falls during a storm, blocking your driveway, you can cut it into pieces with a chainsaw.
While a hand saw works by being manually pulled back and forth, cutting wood with its sharp metal teeth, a chainsaw's cutting power comes from a metal chain that rotates around the blade. Most chainsaws have a small gasoline-powered motor and are very portable. The original chainsaw was an early 1800s surgical tool used to cut bone; by the 1830s, the word also included saws for cutting wood.