Tetratomic

1. a. Having a valence of four; quadrivalent; tetravalent; sometimes, in a specific sense, having four hydroxyl groups, whether acid or basic.
2. a. Consisting of four atoms; having four atoms in the molecule, as phosphorus and arsenic.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.