a.

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

   这些发展使社会生活发生了根本变化。

2. 原本的，与生俱来的
3. 极端的，过激的；激进的；激进派的
   I do not share his radical views.

   我不同意他的激进观点。

4. 【数】根的
5. 【植】根生的
6. 【语】词根的

n.[C]

1. 根部；基础；基本原理
2. （常大写）激进分子；激进党派成员
   He was a political radical.

   他曾是政治上的激进分子。

3. 【数】根数，根式；根号
4. 【语】词根，词干
   Love is the radical of lovely, loveliness, and loving.

   love是lovely, loveliness及loving的词根。

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

   你可以根据部首查找汉字。

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.