The Collaborative International Dictionary of English v.0.48:

Nitrohydrochloric \Ni`tro*hy`dro*chlo"ric\, a. [Nitro- +
   hydrochloric.] (Chem.)
   Of, pertaining to, or containing, nitric and hydrochloric
   acids.
   [1913 Webster]

   Nitrohydrochloric acid, a mixture of nitric and
      hydrochloric acids, usually in the proportion of one part
      of the former to three of the latter, and remarkable for
      its solvent action on gold and platinum; -- called also
      aqua regia, and nitromuriatic acid.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nitrohydrochloric acid
    n 1: a yellow fuming corrosive mixture of nitric and
         hydrochloric acid that dissolves metals (including gold)
         [syn: aqua regia, nitrohydrochloric acid]