radical |ˈradikəl| adjective
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
• Mathematics 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.
• Music belonging to the root of a chord.
• Botany of, or springing direct from, the root or stem base of a plant.
4. [usu. as exclam. ] informal very good; excellent : Okay, then. Seven o'clock.
Radical! noun
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. Chemistry a group of atoms behaving as a unit in a number of compounds. See also free radical . [ORIGIN: early 19th cent.: from French.]
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. Mathematics a quantity forming or expressed as the root of another.
• a radical sign.