Noun

• S: (n) group, radical, chemical group ((chemistry) two or more atoms bound together as a single unit and forming part of a molecule)
• S: (n) free radical, radical (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"
• S: (n) radical (a person who has radical ideas or opinions)
• S: (n) radical ((mathematics) a quantity expressed as the root of another quantity)
• S: (n) radical (a character conveying the lexical meaning of a logogram)
• S: (n) 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"

Adjective

• S: (adj) extremist, radical, ultra ((used of opinions and actions) far beyond the norm) "extremist political views"; "radical opinions on education"; "an ultra conservative"
• S: (adj) revolutionary, radical (markedly new or introducing radical change) "a revolutionary discovery"; "radical political views"
• S: (adj) radical (arising from or going to the root or source) "a radical flaw in the plan"
• S: (adj) radical (of or relating to or constituting a linguistic root) "a radical verb form"
• S: (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"