a.

1. 根本的，基本的；徹底的
   These developments have effected a radical change in social life.

   這些發展使社會生活發生了根本變化。

2. 原本的，與生俱來的
3. 極端的，過激的；激進的；激進派的
   I do not share his radical views.

   我不同意他的激進觀點。

4. 【數】根的
5. 【植】根生的
6. 【文】詞根的

n.[C]

1. 根部；基礎；基本原理
2. （常大寫）激進分子；激進黨派成員
   He was a political radical.

   他曾是政治上的激進分子。

3. 【數】根數，根式；根號
4. 【文】詞根，詞幹
   Love is the radical of lovely, loveliness, and loving.

   love是lovely, loveliness及loving的詞根。

5. （漢字的）偏旁，部首
   You can look up a character under its radical.

   你可以根據部首查找漢字。

adj.

1. relating to or affecting the fundamental nature of something.
   ▸innovative or progressive.
2. (of surgery) thorough and intended to be completely curative.
3. advocating thorough political or social reform; politically extreme.
   ▸Brit. historical belonging to an extreme section of the Liberal party in the 19th century.
4. Mathematics  of the root of a number or quantity.
5. denoting or relating to the roots of a word.
6. Music  belonging to the root of a chord.
7. Botany  of or coming from the root or stem base of a plant.
8. N. Amer. informal excellent.

n.

1. an advocate of radical political or social reform.
2. Chemistry  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 Chinese characters constituting semantically or functionally significant elements in the composition of other characters.
4. Mathematics  a quantity forming or expressed as the root of another.