Definition of Radical

Adjective: radical ra-di-kul

(used of opinions and actions) far beyond the norm
"radical opinions on education";
- extremist, ultra
Markedly new or introducing fundamental change
"radical political views";
- revolutionary
Arising from or going to the root or source
"a radical flaw in the plan"
(linguistics) of or relating to or constituting a linguistic root
"a radical verb form"
(botany) especially of leaves; located at the base of a plant or stem; especially arising directly from the root or rootstock or a root-like stem
"radical leaves";
- basal

Noun: radical ra-di-kul

(chemistry) two or more atoms bound together as a single unit and forming part of a molecule
- group, chemical group
An atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule that has lost an electron and will stabilize itself by stealing an electron from a nearby molecule
"in the body free radicals are high-energy particles that ricochet wildly and damage cells";
- free radical
A person who has radical ideas or opinions
(mathematics) a quantity expressed as the root of another quantity
A character conveying the lexical meaning of a logogram
(linguistics) the form of a word after all affixes are removed
"thematic vowels are part of the radical";
- root, root word, base, stem, theme