potassium permanganate

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

• noun A dark purple crystalline compound, KMnO₄, used as an oxidizing agent and disinfectant and in deodorizers and dyes.

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

• noun chemistry KMnO4, the most readily available commercial permanganate; it is used as an oxidizing agent both in industry and in the analytical laboratory.

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

• noun a poisonous salt that forms dark purple crystals and is purple-red when dissolved in water; used as an oxidizing and bleaching agent and as a disinfectant and antiseptic