The Collaborative International Dictionary of English v.0.48:
Carbonyl \Car"bon*yl\, n. [Carbon + -yl.] (Chem.)
The radical (=CO), occuring, always combined, in many
compounds, as the aldehydes, the ketones, urea, carbonyl
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.
[1913 Webster +PJC]