hydrogen peroxide

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A colorless, heavy, strongly oxidizing liquid, H₂O₂, capable of reacting explosively with combustibles and used principally in aqueous solution as a mild antiseptic, bleaching agent, oxidizing agent, and laboratory reagent.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun inorganic chemistry A colourless liquid, H2O2, soluble in water, used as a mild antiseptic, bleaching agent (especially for bleaching hair), oxidizing agent and chemical reagent.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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