- In chemistry, a radical is a group of atoms,
either in a compound or existing alone
in which all the atomic valences are not satisfied by chemical bonding.
Thus, removal of a hydrogen atom from methane, CH4, gives
the methyl radical CH3. The term is usually taken to mean
a free radical, that is, one existing
free for a short time in a reaction.
- In mathematics, a radical is the root of a
number or quantity. The radical sign is √, or more generally n√.
It seems to have been first used in 1525 by Christoff Rudolff (1499–1545)
in his Die Coss. Another way of expressing the nth
of a number x1/n.