poly·atom·ic /-əˈtɑmɪk/
  (a.)多原子的
  Pol·y·a·tom·ic a.  Chem. (a) Having more than one atom in the molecule; consisting of several atoms. (b) Having a valence greater than one. [Obs.]
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  polyatomic
       adj : of or relating to a molecule made up of more than two atoms