The Collaborative International Dictionary
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 Worlds War it was also used as a poisonous gas in combat.
Carbonyl \Car"bon*yl\, n. [Carbon + -yl.] (Chem.) The radical (CO)'', occuring, always combined, in many compounds, as the aldehydes, the ketones, urea, carbonyl chloride, etc.
Note: Though denoted by a formula identical with that of carbon monoxide, it is chemically distinct, as carbon seems to be divalent in carbon monoxide, but tetravalent in carbonyl compounds.
Carbonyl chloride (Chem.), a colorless gas, COCl2, of offensive odor, and easily condensable to liquid. It is formed from chlorine and carbon monoxide, under the influence of light, and hence has been called phosgene, or phosgene gas; -- called also carbon oxychloride. It is used in chemical synthesis, and was also used as a poison gas in World War I.