D defs.my
Entry 1 sense Webster, 1913

Monatomic

/mänˌ-ət-äm'-ĭk/ · Mon·a·tom·ic · IPA /mˌɑnətˈɑmɪk/
01 adv. Consisting of, or containing, one atom; as, the molecule of mercury is monatomic.
  1. 1.
    Consisting of, or containing, one atom; as, the molecule of mercury is monatomic.(Chem.)