Radical is derived from the Latin word radix, which means "root". In various fields of endeavor, it can mean:

Sciences

• 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 radical of an algebraic group is a concept in algebraic group theory.
  • the radical of an ideal is an important concept in abstract algebra.
• in linguistics, a part of a Chinese character (see radical (Chinese character)).

Social sciences

• in sociology:
  • one who advocates thoroughgoing analysis or change "at the root"
• in politics:
  • can refer to a supporter of a revolutionary social movement
  • can refer to a counterpart to reactionary; see Radical Republican
  • can refer to member of a Radical Party
  • can refer to a progressive liberal, like e.g. the Radicals, a group of left-wing MPs in the 19th-century British Parliament