A person who advocates for thorough or complete political or social reform. The radicals in the group were pushing for immediate changes to the system.
Chemistry: an atom, molecule, or group of atoms that possesses at least one unpaired electron, making it highly reactive; a free radical. Free radicals such as the hydroxyl radical readily react with biological molecules.
The root of a word, from which other words can be derived. In linguistics, the radical of the word 'unhappiness' is 'happy'.
A mathematical expression indicating the root of a number. The radical sign is used to denote the square root of a number.