1) Binary 2) Matter 3) Substance 
Molecule composed of two atoms of the same kind.
• (a.) Having two replaceable atoms or radicals. • (a.) Containing two atoms.
Elements that are present in the gaseous state as molecules composed of two atoms. For example: O2, N2, Cl2 and H2 are diatomic.
(di″ә-tom´ik) containing two atoms. dibasic.
Di`a·tom'ic (dī`ȧ*tŏm'ĭk) adjective [ Prefix di- + atomic .] (Chemistry) (a) Containing two atoms. (b) Having two replaceable atoms or radicals. 
Type: Term Pronunciation: dī′ă-tom′ik Definitions: 1. Denoting a compound with a molecule made up of two atoms. 2. Denoting any ion or atomic grouping composed of two atoms only.
[adj] - of or relating to a molecule made up of two atoms
adjective of or relating to a molecule made up of two atoms; `a diatomic molecule`
having two atoms in the molecule. · containing two replaceable atoms or groups; binary.