The Collaborative International Dictionary of English v.0.48:

Carbamic \Car*bam"ic\ (k[aum]r*b[a^]m"[i^]k), a. [Carbon +
   amido.] (Chem.)
   Pertaining to an acid so called.
   [1913 Webster]

   Carbamic acid (Chem.), an amido acid, H2N.CO2.H, not
      existing in the free state, but occurring as a salt of
      ammonium in commercial ammonium carbonate; -- called also
      amido formic acid.
      [1913 Webster]

WordNet (r) 3.0 (2006):

carbamic acid
    n 1: an acid that is known only by virtue of its salts (as
         ammonium carbamate) or its esters (as urethane)