radical

Dictionary definition · radical

(chemistry) two or more atoms bound together as a single unit and forming part of a molecule
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"
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 stem"

(used of opinions and actions) far beyond the norm"extremist political views"
markedly new or introducing radical change"a revolutionary discovery"
arising from or going to the root or source"a radical flaw in the plan"
of or relating to or constituting a linguistic root"a radical verb form"
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"basal placentation"

Source: Open English WordNet (CC BY 4.0).