Rad·i·cal a.
 1. Of or pertaining to the root; proceeding directly from the root.
 2. Hence: Of or pertaining to the root or origin; reaching to the center, to the foundation, to the ultimate sources, to the principles, or the like; original; fundamental; thorough-going; unsparing; extreme; as, radical evils; radical reform; a radical party.
    The most determined exertions of that authority, against them, only showed their radical independence.   --Burke.
 3. Bot. (a) Belonging to, or proceeding from, the root of a plant; as, radical tubers or hairs. (b) Proceeding from a rootlike stem, or one which does not rise above the ground; as, the radical leaves of the dandelion and the sidesaddle flower.
 4. Philol. Relating, or belonging, to the root, or ultimate source of derivation; as, a radical verbal form.
 5. Math. Of or pertaining to a radix or root; as, a radical quantity; a radical sign. See below.
 Radical axis of two circles. Geom. See under Axis.
 Radical pitch, the pitch or tone with which the utterance of a syllable begins. --Rush.
 Radical quantity Alg., a quantity to which the radical sign is prefixed; specifically, a quantity which is not a perfect power of the degree indicated by the radical sign; a surd.
 Radical sign Math., the sign √ (originally the letter r, the initial of radix, root), placed before any quantity, denoting that its root is to be extracted; thus, √a, or √(a + b). To indicate any other than the square root, a corresponding figure is placed over the sign; thus, a, indicates the third or cube root of a.
 Radical stress Elocution, force of utterance falling on the initial part of a syllable or sound.
 Radical vessels Anat., minute vessels which originate in the substance of the tissues.
 Syn: -- Primitive; original; natural; underived; fundamental; entire.
 Usage: -- Radical, Entire. These words are frequently employed as interchangeable in describing some marked alteration in the condition of things. There is, however, an obvious difference between them. A radical cure, reform, etc., is one which goes to the root of the thing in question; and it is entire, in the sense that, by affecting the root, it affects in an appropriate degree the entire body nourished by the root; but it may not be entire in the sense of making a change complete in its nature, as well as in its extent. Hence, we speak of a radical change; a radical improvement; radical differences of opinion; while an entire change, an entire improvement, an entire difference of opinion, might indicate more than was actually intended. A certain change may be both radical and entire, in every sense.