- In chemistry, a group of elements or atoms usually passing intact from one compound to another, but usually incapable of prolonged existence in a free state (methyl, CH3); in chemical formulas, a radical is often distinguished by being enclosed in parentheses or brackets.
- Thorough or extensive; relating or directed to the extirpation of the root or cause of a morbid process; a radical operation.
- Denoting treatment by extreme, drastic, or innovative, as opposed to conservative, measures.
- A functional group in a molecule or molecular entity.
Synonym(s): free radical
[L. radix (radic-), root]