As an adjective, radical means very new, extreme, or different from traditional ideas or ways of doing things. As a noun, it refers to a person who strongly supports major changes in society or politics.
It comes from Late Latin “radicalis,” meaning “of or relating to a root,” from Latin “radix,” meaning “root.” The sense of “fundamental” or “extreme” grew from the idea of going to the root of a problem or system.
“Radical” literally started out meaning “root‑like,” so a radical idea is one that digs right down to the roots of a system. The same root “radix” also gives us “radish,” which is a root vegetable, and “eradicate,” which means to pull something out by the roots.
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