tetratomic

[ te-truh-tom-ik ]
/ ˌtɛ trəˈtɒm ɪk /

adjective Chemistry.

having four atoms per molecule, especially of a specified kind.
having four replaceable atoms or radicals.

British Dictionary definitions for tetratomic

tetratomic
/ (ˌtɛtrəˈtɒmɪk) /

adjective

composed of four atoms or having four atoms per molecule phosgene has tetratomic molecules