radical

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rad·i·cal / ˈradikəl/ • adj. 1. (esp. of change or action) relating to or affecting the fundamental nature of something; far-reaching or thorough: a radical overhaul of the existing regulatory framework. ∎  forming an inherent or fundamental part of the nature of someone or something: the assumption of radical differences between the mental attributes of literate and nonliterate peoples. ∎  (of surgery or medical treatment) thorough and intended to be completely curative. ∎  characterized by departure from tradition; innovative or progressive: a radical approach to electoral reform. 2. advocating thorough or complete political or social reform; representing or supporting an extreme section of a political party: a radical American activist. ∎  (of a measure or policy) following or based on such principles. 3. of or relating to the root of something, in particular: ∎  Math. of the root of a number or quantity. ∎  denoting or relating to the roots of a word. ∎  denoting the semantic or functional class of a Chinese character. ∎  Mus. belonging to the root of a chord. ∎  Bot. of, or springing direct from, the root or stem base of a plant. 4. [usu. as interj.] inf. very good; excellent: Okay, then. Seven o'clock. Radical! • n. 1. a person who advocates thorough or complete political or social reform; a member of a political party or part of a party pursuing such aims. 2. Chem. a group of atoms behaving as a unit in a number of compounds. See also free radical. 3. the root or base form of a word. ∎  any of the basic set of 214 Chinese characters constituting semantically or functionally significant elements in the composition of other characters and used as a means of classifying characters in dictionaries. 4. Math. a quantity forming or expressed as the root of another. ∎  a radical sign. DERIVATIVES: rad·i·cal·ism / -ˌlizəm/ n. (in sense 1 of the noun ). rad·i·cal·ly / -ik(ə)lē/ adv. a radically different approach. rad·i·cal·ness n.

radical in chemistry, group of atoms that are joined together in some particular spatial structure and that take part in most chemical reactions as a single unit. Important inorganic radicals include ammonium, NH ₄ ; carbonate, CO ₃  ; chlorate, ClO ₃ , and perchlorate, ClO ₄  ; cyanide, CN; hydroxide, OH; nitrate, NO ₃ ; phosphate, PO ₄ ; silicate, SiO ₃ (meta) or SiO ₄ (ortho); and sulfate, SO ₄ . The use of these radicals simplifies the naming and description of inorganic compounds, since such usage does not consider the electronic charge on the group. (When ions are dealt with, electronic charge must be considered.) In organic chemistry, the term radical is sometimes used synonymously with group; e.g., the group CH ₃ is sometimes called the methyl radical instead of the methyl group. This use is limited chiefly to alkyl groups and aryl groups ; it is usually not applied to functional groups , such as carbonyl. Because the term radical easily could be taken to mean a free radical , the term group is preferred by some.

radical advocating thorough or complete political or social reform; representing or supporting an extreme or progressive section of a political party; the word in this sense is first recorded in Shelley' Oedipus Tyrannus (1820), ‘Kings and laurelled Emperors, Radical butchers’. In a letter of 1832, John Stuart Mill refers to, ‘Several friends of mine, radical-utilitarians of a better than the ordinary sort.’

Radical is recorded from late Middle English (in the senses ‘forming the root’ and ‘inherent’), and comes ultimately from Latin radix, radic- ‘root’.
radical chic a fashionable affectation of radical left-wing views or an associated style of dress or life; term coined by the American writer Tom Wolfe (1931– ).

radical pert. to the moisture inherent in animals and plants XIV; (math., philol., etc.) pert. to a root or radix; inherent, fundamental XVI; going to the root or origin, thorough XVII (r. reform XVIII); sb. radical element XVII; advocate of ‘radical reform’ XIX. — late L. rādīcālis, f. L. rādīx, rādīc- root; see -AL1.
Hence radicalism XIX.

radical Applied to a leaf that arises from a rhizome or from the base of a stem.

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