The Collaborative International Dictionary of English v.0.48:

phosgene \phos"gene\ (f[o^]s"j[=e]n or f[o^]z"j[=e]n), n.
   (Chem.)
   A reactive chemical substance (COCl2), also called
   carbonyl choride, used in synthesis of numerous substances.
   In the First World War it was also used as a poisonous gas in
   combat.
   [PJC]