A chainsaw is a tool for cutting wood. A motor drives a metal chain that runs around a long bar; the chain has sharp teeth, so it bites through trees and logs much faster than a saw you move with your hands. People use it to cut down trees, cut logs into pieces, and clear fallen wood after a storm. It is loud, heavy, and dangerous — you need training, a firm grip, and safety gear, because a moment of carelessness can cut a person as easily as a branch. Though actually, the word is also a verb: to chainsaw a tree is to cut it with one. In films and games a chainsaw can be a scary weapon, but in real life it is a work tool for farmers, gardeners, and forest workers, not a kitchen word and not a school word.