- radical ► ADJECTIVE 1) relating to or affecting the fundamental nature of something. 2) advocating thorough political or social reform; politically extreme. 3) departing from tradition; innovative or progressive. 4) (of surgery) thorough and intended to be completely curative. 5) Mathematics of the root of a number or quantity. 6) of or coming from the root or stem base of a plant. 7) informal, chiefly N. Amer. excellent.► NOUN 1) an advocate of radical political or social reform. 2) Chemistry a group of atoms behaving as a unit in a number of compounds.DERIVATIVES radicalism noun radicalize (also radicalise) verb radically adverb radicalness noun.ORIGIN Latin radicalis, from radix 'root' .
English terms dictionary. 2015.