'Polyatomic' definitions:

Definition of 'polyatomic'

(from WordNet)
adjective
Of or relating to a molecule made up of more than two atoms

Definition of 'Polyatomic'

From: GCIDE
  • Polyatomic \Pol`y*a*tom"ic\, a. [Poly- + atomic.] (Chem.) (a) Having more than one atom in the molecule; consisting of several atoms. (b) Having a valence greater than one. [Obs.] [1913 Webster]