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
   chloride, etc.
   [1913 Webster]

   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.
         [1913 Webster]

   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]