radical has 12 distinct synonyms spread across 6 of its 11 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is cauline.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
(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
2 of the 11 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for radical.
Synonyms, antonyms and the broader and narrower relations for radical come from Princeton University’s WordNet. Full sources and licences.