Definition of: radical

(rad′i·kəl) adjective
1. Of, proceeding from, or pertaining to the root or foundation; essential; fundamental; inherent; basic.
2. Thoroughgoing; unsparing; extreme: a radical operation; radical measures.
3. Math. Pertaining to the root or roots of a number.
4. In philology, belonging or referring to a root or a root syllable; underived.
5. Bot. Springing from or belonging or relating to the root: radical leaves.
6. Chem. Pertaining to a radical.
7. Of or pertaining to political radicals.
—noun
1. One who carries his theories or convictions to their furthest application; an extremist.
2. In politics, one who advocates wide–spread governmental changes and reforms at the earliest opportunity.
3. The primitive or underived part of a word; a primitive word or syllable; a root; radicle.
4. Math. a A quantity of which the root is to be extracted or used in calculation; a radical expression, b The radical sign.
5. Chem. A fundamental constituent or part of a compound; specifically, a group of atoms which acts as a unit in a compound and may either pass unchanged through a series of reactions or be replaced as though it were a single atom. ♦ Homophone: radicle. [<LL radicalis having roots <L radix, radicis root]
—rad′i·cal·ness noun Synonyms (adj.): basic, complete, constitutional, entire, essential, extreme, fundamental, ingrained, inherent, innate, native, natural, organic, original, perfect, positive, primary, primitive, thorough, thoroughgoing, total. The widely divergent senses in which the word radical is used, by which it can be at sometime interchanged with any word in the above list, are all formed upon the one primary sense of that which is connected with the root (Latin radix). A radical difference is one that springs from the root, and is thus constitutional, essential, fundamental, organic, original; a radical change is one that does not stop at the surface, but reaches down to the very root, and is entire, thorough, total; since the majority find superficial treatment of any matter the easiest and most comfortable, radical measures, which strike at the root of evil or need, are apt to be looked upon as extreme. See NATURAL. Antonyms: compromising, conciliatory, conservative, half–way, inadequate, incomplete, moderate, palliative, partial, superficial.