adj. & n.
--adj.
1. of the root or roots; fundamental (a radical error).
2 far-reaching; thorough; going to the root (radical change).
3 a advocating thorough reform; holding extreme political views; revolutionary. b (of a measure etc.) advanced by or according to principles of this kind.
4 forming the basis; primary (the radical idea).
5 Math. of the root of a number or quantity.
6 (of surgery etc.) seeking to ensure the removal of all diseased tissue.
7 of the roots of words.
8 Mus. belonging to the root of a chord.
9 Bot. of, or springing direct from, the root.
10 hist. belonging to an extreme section of the Liberal party.
11 US hist. seeking extreme anti-South action at the time of the Civil War.
--n.
1. a person holding radical views or belonging to a radical party.
2 Chem. a a free radical. b an element or atom or a group of these normally forming part of a compound and remaining unaltered during the compound's ordinary chemical changes.
3 the root of a word.
4 a fundamental principle; a basis.
5 Math. a a quantity forming or expressed as the root of another. b a radical sign.
Phrases and idioms:
radical sign indicating the square, cube, etc., root of the number following.
Derivatives:
radicalism n. radicalize v.tr. & intr. (also -ise). radicalization n. radically adv. radicalness n.
Etymology: ME f. LL radicalis f. L radix radicis root