RAD'ICAL, a. [L. radicalis, from radix, root. See Race and Ray.]1. Pertaining to the root or origin; original; fundamental; as a radical truth or error; a radical evil; a radical difference of opinions or systems.2. Implanted by nature; native; constitutional; as the radical moisture of a body.3. Primitive; original; underived; uncompounded; as a radical word.4. Serving to origination.5. In botany, proceeding immediately from the root; as a radical leaf or peduncle.
RAD'ICAL, n.1. In philology, a primitive word; a radix, root, or simple underived uncompounded word.2. A primitive letter; a letter that belongs to the radix.3. in chimistry, an element, or a simple constituent part of a substance, which is incapable of decomposition.That which constitutes the distinguishing part of an acid, by its union with oxygen.Compound radical is the base of an acid composed of two or more substances. Thus a vegetable acid having a radical composed of hydrogen and carbon, is said to be an acid with a compound radical.Radical quantities, in algebra, quantities whose roots may be accurately expressed in numbers. The term is sometimes extended to all quantities under the radical sign.