The Collaborative International Dictionary of English v.0.48:

Isocyanic \I`so*cy*an"ic\, a. [Iso- + cyanic.] (Chem.)
   Designating an acid isomeric with cyanic acid.
   [1913 Webster]

   Isocyanic acid, an acid metameric with cyanic acid, and
      resembling it in its salts. It is obtained as a colorless,
      mobile, unstable liquid by the heating cyanuric acid.
      Called technically carbimide.
      [1913 Webster]