The Collaborative International Dictionary of English v.0.48:

Flagon \Flag"on\, n. [F. flacon, for flascon, fr. OF. flasche,
   from LL. flasco. See Flask.]
   A vessel with a narrow mouth, used for holding and conveying
   liquors. It is generally larger than a bottle, and of leather
   or stoneware rather than of glass.
   [1913 Webster]

         A trencher of mutton chops, and a flagon of ale.
                                                  --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flagon
    n 1: a large metal or pottery vessel with a handle and spout;
         used to hold alcoholic beverages (usually wine)