1. (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
2. an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule than 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. a person who has radical ideas or opinions
4. a character conveying the lexical meaning of a logogram
5. a sign placed in front of an expression to denote that a root is to be extracted
6. (linguistics) the form of a word after all affixes are removed;