/fee'neuh thuy"euh zeen', -zin/ , n.
1. Chem. a grayish-green to greenish-yellow, crystalline, water-insoluble solid, C 12 H 9 NS, used chiefly as an insecticide and vermifuge, and in the synthesis of pharmaceuticals.
2. Pharm. any of a class of medications used principally to treat psychotic symptoms, as delusions or hallucinations, and excessive excitability.
[ 1890-95; PHENO- + THIAZINE ]