1. (noun)group, radical, chemical group (chemistry) two or more atoms bound together as a singleunit and forming part of a molecule
2. (noun)free radical, radical an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygenmolecule 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"
3. (noun)radical a person who has radical ideas or opinions
4. (noun)radical (mathematics) a quantity expressed as the root of another quantity
6. (noun)root, root word, base, stem, theme, radical (linguistics) the form of a word after all affixes are removed
"thematic vowels are part of the stem"
7. (adj)extremist, radical, ultra (used of opinions and actions) far beyond the norm "extremist political views"; "radical opinions on education"; "an ultra conservative"
8. (adj)revolutionary, radical markedly new or introducing radicalchange "a revolutionary discovery"; "radical political views"
9. (adj)radical arising from or going to the root or source "a radical flaw in the plan"
10. (adj)radical of or relating to or constituting a linguistic root "a radical verb form"
11. (adj)radical, basal 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"; "radical leaves"