thioxanthone

from The Century Dictionary.

• noun A yellow compound, , prepared by the action of sulphuric acid on phenyl-thiosalicylic acid. It crystallizes in needles, melts at 209° C., and boils at 371–373° C. under 715 millimeters pressure.

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

• noun organic chemistry A tricyclic ketone derivative of thioxanthene having a carbonyl group opposite the sulfur atom