Source : Webster's Revised Unabridged Dictionary (1913)

Superoxide \Su`per*ox"ide\, n. (Chem.)
   See {Peroxide}. [Obs.]

Source : WordNet®

superoxide
     n 1: a metallic oxide containing the univalent anion O2-
     2: the univalent anion O2-; "much of the O2 supporting cellular
        respiration is reduced to the superoxide anion O2-" [syn:
        {superoxide anion}]