Radical /(răd"ĭ*kal)/

Rad·i·cal

Radical

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.
  3. Belonging to, or proceeding from, the root of a plant; as, radical tubers or hairs. (Bot.)
  4. Relating, or belonging, to the root, or ultimate source of derivation; as, a radical verbal form. (Philol.)
  5. Of or pertaining to a radix or root; as, a radical quantity; a radical sign. See below. (Math.)

Phrases & Compounds
Radical axis of two circles
See under Axis.
Radical pitch
the pitch or tone with which the utterance of a syllable begins.
Radical quantity
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
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
force of utterance falling on the initial part of a syllable or sound.
Radical vessels
minute vessels which originate in the substance of the tissues.
Syn. -- Primitive; original; natural; underived; fundamental; entire.

-- 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.

Radical

n.
  1. A primitive word; a radix, root, or simple, underived, uncompounded word; an etymon. (Philol.)
    The words we at present make use of, and understand only by common agreement, assume a new air and life in the understanding, when you trace them to their radicals, where you find every word strongly stamped with nature; full of energy, meaning, character, painting, and poetry.
    — Cleland.
  2. One who advocates radical changes in government or social institutions, especially such changes as are intended to level class inequalities; -- opposed to conservative. (Politics)
    In politics they [the Independents] were, to use the phrase of their own time, “Root-and-Branch men,” or, to use the kindred phrase of our own, Radicals.
  3. A characteristic, essential, and fundamental constituent of any compound; hence, sometimes, an atom. (Chem.)
    As a general rule, the metallic atoms are basic radicals, while the nonmetallic atoms are acid radicals.
    — J. P. Cooke.
  4. Specifically, a group of two or more atoms, not completely saturated, which are so linked that their union implies certain properties, and are conveniently regarded as playing the part of a single atom; a residue; -- called also a compound radical. Cf. Residue.
  5. A radical quantity. See under Radical, a. (Alg.)
    An indicated root of a perfect power of the degree indicated is not a radical but a rational quantity under a radical form.
  6. A radical vessel. See under Radical, a. (Anat.)