thionine

from The Century Dictionary.

• noun A brownish-black dye, , prepared by the action of hydrogen sulphid and ferric chlorid on or-thophenylene-diamine-hydrochlorid. It crystallizes in plates, gives with alcohol a violet to violet-red solution with a reddish-brown fluorescence, and is largely used for staining microscopic objects. Also called amiminothiodiphenylimine, phenylene violet, and Lauth' s violet.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) An artificial red or violet dyestuff consisting of a complex sulphur derivative of certain aromatic diamines, and obtained as a dark crystalline powder; -- called also phenylene violet.

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

• noun chemistry An artificial red or violet dyestuff consisting of a complex sulfur derivative of certain aromatic diamines.