The Collaborative International Dictionary of English v.0.48:

Cognac \Co"gnac`\, n. [F.]
   A kind of French brandy, so called from the town of Cognac.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Cognac
    n 1: high quality grape brandy distilled in the Cognac district
         of France