Source : Webster's Revised Unabridged Dictionary (1913)

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

   {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}.

Source : WordNet®

isocyanic acid
     n : an acid known only in the form of its esters