An Etymological Dictionary of Astronomy and Astrophysics

1. Math.: The indicated root of a quantity, as denoted by an expression written under the → radical sign.
   

2. Chemistry: A group of atoms present in a series of compounds which conserves its identity in the course of chemical changes which affect the rest of the molecule.
   For example, the
   → cyano radical and → hydroxyl group.

Etymology (EN): M.E., from L.L. radicalis “of or having roots,” from → radix “root.”

Etymology (PE): → root.