a. [ F., fr. L. radicalis having roots, fr. radix, -icis, a root. See Radix. ] 1. Of or pertaining to the root; proceeding directly from the root. [ 1913 Webster ]

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. [ 1913 Webster ]

The most determined exertions of that authority, against them, only showed their radical independence. Burke. [ 1913 Webster ]

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. [ 1913 Webster ]

4. (Philol.) Relating, or belonging, to the root, or ultimate source of derivation; as, a radical verbal form. [ 1913 Webster ]

5. (Math.) Of or pertaining to a radix or root; as, a radical quantity; a radical sign. See below. [ 1913 Webster ]

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, &cuberoot_;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. [ 1913 Webster ]

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. [ 1913 Webster ]

n. 1. (Philol.) (a) A primitive word; a radix, root, or simple, underived, uncompounded word; an etymon. (b) A primitive letter; a letter that belongs to the radix. [ 1913 Webster ]

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. [ 1913 Webster ]

2. (Politics) One who advocates radical changes in government or social institutions, especially such changes as are intended to level class inequalities; -- opposed to conservative. [ 1913 Webster ]

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. Macaulay. [ 1913 Webster ]

3. (Chem.) (a) A characteristic, essential, and fundamental constituent of any compound; hence, sometimes, an atom. [ 1913 Webster ]

As a general rule, the metallic atoms are basic radicals, while the nonmetallic atoms are acid radicals. J. P. Cooke. [ 1913 Webster ]

(b) 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. [ 1913 Webster ]

4. (Alg.) A radical quantity. See under Radical, a. [ 1913 Webster ]

An indicated root of a perfect power of the degree indicated is not a radical but a rational quantity under a radical form. Davies & Peck (Math. Dict.) [ 1913 Webster ]

5. (Anat.) A radical vessel. See under Radical, a. [ 1913 Webster ]

n. [ Cf. F. radicalisme. ] The quality or state of being radical; specifically, the doctrines or principles of radicals in politics or social reform. [ 1913 Webster ]

Radicalism means root work; the uprooting of all falsehoods and abuses. F. W. Robertson. [ 1913 Webster ]

n. 1. Germinal principle; source; origination. [ Obs. ] Sir T. Browne. [ 1913 Webster ]

2. Radicalness; relation to a root in essential nature or principle. [ 1913 Webster ]

adv. 1. In a radical manner; at, or from, the origin or root; fundamentally; as, a scheme or system radically wrong or defective. [ 1913 Webster ]

2. Without derivation; primitively; essentially. [ R. ] [ 1913 Webster ]

These great orbs thus radically bright. Prior. [ 1913 Webster ]

n. Quality or state of being radical. [ 1913 Webster ]