rad·i·cal /ˈrædɪkəl/
 激進分子,語根,基礎(a.)激進的,根本的,基本的,根的


 rad·i·cal /ˈrædɪkəl/ 形容詞
 根,基,原子團,根本的


 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.

From: Webster's Revised Unabridged Dictionary (1913)

 Rad·i·cal 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.
    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. Politics One who advocates radical changes in government or social institutions, especially such changes as are intended to level class inequalities; -- opposed to conservative.
    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.
 3. Chem. (a) A characteristic, essential, and fundamental constituent of any compound; hence, sometimes, an atom.
    As a general rule, the metallic atoms are basic radicals, while the nonmetallic atoms are acid radicals.   --J. P. Cooke.
 (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.
 4. Alg. A radical quantity. See under Radical, a.
    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.)
 5. Anat. A radical vessel. See under Radical, a.

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From: WordNet (r) 2.0

 radical
      adj 1: (used of opinions and actions) far beyond the norm;
             "extremist political views"; "radical opinions on
             education"; "an ultra conservative" [syn: extremist,
              ultra]
      2: markedly new or introducing radical change; "a revolutionary
         discovery"; "radical political views" [syn: revolutionary]
      3: arising from or going to the root; "a radical flaw in the
         plan"
      4: of or relating to or constituting a linguistic root; "a
         radical verb form"
      5: especially of leaves; located at the base of a plant or
         stem; especially arising directly from the root or
         rootstock or a root-like stem; "basal placentation";
         "radical leaves" [syn: basal] [ant: cauline]
      n 1: (chemistry) two or more atoms bound together as a single
           unit and forming part of a molecule [syn: group, {chemical
           group]
      2: an atom or group of atoms with at least one unpaired
         electron; in the body it is usually an oxygen molecule
         than has lost an electron and will stabilize itself by
         stealing an electron from a nearby molecule; "in the body
         free radicals are high-energy particles that ricochet
         wildly and damage cells" [syn: free radical]
      3: a person who has radical ideas or opinions
      4: a character conveying the lexical meaning of a logogram
      5: a sign placed in front of an expression to denote that a
         root is to be extracted [syn: radical sign]
      6: (linguistics) the form of a word after all affixes are
         removed; "thematic vowels are part of the stem" [syn: root,
          root word, base, stem, theme]