A defoliant is a chemical that makes plants drop all their leaves. Armies have used it in war to strip a forest so they can see the ground and anyone hiding there. The mix called Agent Orange, used in the Vietnam War, is the example history classes keep returning to: it took the leaves, and it also made many people very sick later. Farmers have used milder leaf-stripping chemicals too, but when English speakers say defoliant they usually mean the wartime kind. It is a news-and-history word, not kitchen talk. It names the chemical, not a machine and not a person.