The Collaborative International Dictionary of English v.0.48:

Peroxide \Per*ox"ide\, n. (Chem.)
   An oxide containing more oxygen than some other oxide of the
   same element. Formerly peroxides were regarded as the highest
   oxides. Cf. Per-, 2.
   [1913 Webster]

WordNet (r) 3.0 (2006):

peroxide
    n 1: a viscous liquid with strong oxidizing properties; a
         powerful bleaching agent; also used (in aqueous solutions)
         as a mild disinfectant and (in strong concentrations) as an
         oxidant in rocket fuels [syn: hydrogen peroxide,
         peroxide]
    2: an inorganic compound containing the divalent ion -O-O-
    v 1: bleach with peroxide; "She must peroxide her hair-it looks
         unnaturally blond"

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "peroxide":
   achromatize, blanch, bleach, bleaching powder, chlorine, decolor,
   decolorize, dim, discolor, drain, drain of color, dull, etiolate,
   fade, fume, hydrochloric acid, hydrogen peroxide, lime,
   nitrogen tetroxide, oxalic acid, pale, sodium hypochlorite, sour,
   sulfur dioxide, sulfuric acid, tarnish, tone down, wash out,
   white sour, whiten