Dictionary

(historical: 19th-century Britain) A member of the most progressive wing of the Liberal Party; someone favouring social reform (but generally stopping short of socialism).

(historical: early 20th-century France) A member of an influential, centrist political party favouring moderate social reform, a republican constitution, and secular politics.

A person with radical opinions.

A root (of a number or quantity).

Favoring fundamental change, or change at the root cause of a matter.

Example: His beliefs are radical.

Pertaining to a root (of a plant).

Pertaining to the basic or intrinsic nature of something.

Thoroughgoing; far-reaching.

Example: The spread of the cancer required radical surgery, and the entire organ was removed.