Radical is derived from the Latin word radix, which means "pertaining to the root(s)". In various fields of endeavor, it can mean:
- in sociology:
- one who advocates thoroughgoing analysis or change "at the root"
- in politics:
- (at the extreme) a supporter of a revolutionary social movement
- a counterpart to a conservative; see Radical Republican
- in chemistry, either an atom or molecule with at least one unpaired electron, or a group of atoms, charged or uncharged, that act as a single entity in reaction. These two definitions are not functionally identical. (see radical (chemistry)).
- in mathematics:
- the n-th radical or root of a number a, written as , which is a number whose n-th power is a (see radical (mathematics)).
- the Jacobson radical of a ring, which is an important ideal.
- in linguistics, a part of a Chinese character (see radical (Chinese character)).