The term 'univalent radical' refers to a type of chemical compound that contains only one atom of a particular element. The crossword solution for this term is 'aryl, ' which is an organic compound composed of a single aromatic ring with at least one attached substituent. Aromatic rings are cyclic molecules that contain alternating double and single bonds, and substituents are atoms or groups of atoms that are attached to the ring. Aromatic compounds are often used as solvents, dyes, and pharmaceuticals.