/ ˈrædɪkl; NAmE / adjective , noun
■ adjective [ usually before noun ]
1.
concerning the most basic and important parts of sth; thorough and complete
SYN far-reaching :
the need for radical changes in education
demands for radical reform of the law
radical differences between the sexes
2.
new, different and likely to have a great effect :
radical ideas
a radical solution to the problem
radical proposals
3.
in favour of thorough and complete political or social change :
the radical wing of the party
radical politicians / students / writers
4.
( old-fashioned , NAmE , slang ) very good
► rad·ic·al·ly / -kli; NAmE / adverb :
The new methods are radically different from the old.
Attitudes have changed radically.
■ noun
1.
a person with radical opinions :
political radicals
2.
( chemistry ) a group of atoms that behave as a single unit in a number of compounds
—see also free radical
••
WORD ORIGIN
late Middle English (in the senses forming the root and inherent ): from late Latin radicalis , from Latin radix , radic- root.