peroxide UK /pəˈɹɒksaɪd/US /pəˈɹɑksaɪd/noun 3verb 1forms 3 noun3 •A divalent radical or anion containing two oxygen atoms linked by a covalent bond; any substance containing this group yields hydrogen peroxide when treated with an acid. •Hydrogen peroxide, especially when in an aqueous solution used as a bleach. •Any compound containing the functional group R-O-O-R'.The O–O bond in benzoyl peroxide and the C–N bonds in AIBN homolyze under thermal or photochemical conditions. — 2007 verb1 •To treat (something) with hydrogen peroxide, especially hair in order to bleach it. formsperoxided · peroxiding · peroxides