Relating to or advocating fundamental or revolutionary changes in current practices, conditions, or institutions: radical politics; a radical political theorist.
An individual atom or element as a constituent of a compound was formerly termed a simple radical, as distinct from a group or compound radical. The use of the word for single atoms is now unusual except in referring to free radicals (see sense B.5b).
Relating to or advocating fundamental or revolutionary changes in current practices, conditions, or institutions: radical politics; a radical political theorist.