thiazine

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of a class of organic chemical compounds containing a ring composed of one sulfur atom, one nitrogen atom, and four carbon atoms, used in making dyes.

Wiktionary

1. n. organic chemistry A six-membered heterocycle containing four carbon atoms, one nitrogen and one sulfur atom, and two double bonds; many of its derivatives have important applications

WordNet 3.0

1. n. a compound made up of a ring of four carbon atoms and one sulfur atom and one nitrogen atom