The Collaborative International Dictionary of English v.0.48:

Aqua fortis \A`qua for"tis\ [L., strong water.] (Chem.)
   Nitric acid. [Archaic]
   [1913 Webster]

WordNet (r) 3.0 (2006):

aqua fortis
    n 1: acid used especially in the production of fertilizers and
         explosives and rocket fuels [syn: nitric acid, aqua
         fortis]