Wiktionary
thioxanthene
n. (context organic compound English) The tricyclic heterocycle (sulfur analogue of xanthene) consisting of two benzene rings fused to that of thiopyran
Wikipedia
Thioxanthene
Thioxanthene is a chemical compound in which the oxygen atom in xanthene is replaced with a sulfur atom. It is also related to phenothiazine. Several of its derivatives are used as typical antipsychotics in the treatment of schizophrenia and other psychoses.