Monatomic

[,mɒnә'tɒmik]

(adj.) of or relating to an element consisting of a single atom; 'helium and argon are monatomic gases' .

Typed by Clarissa--From WordNet

(adv.) Consisting of, or containing, one atom; as, the molecule of mercury is monatomic.

(adv.) Having the equivalence or replacing power of an atom of hydrogen; univalent; as, the methyl radical is monatomic.

Checker: Truman