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)

Easton's 1897 Bible Dictionary:

Flagon
   Heb. ashishah, (2 Sam. 6:19; 1 Chr. 16:3; Cant. 2:5; Hos. 3:1),
   meaning properly "a cake of pressed raisins." "Flagons of wine"
   of the Authorized Version should be, as in the Revised Version,
   "cakes of raisins" in all these passages. In Isa. 22:24 it is
   the rendering of the Hebrew _nebel_, which properly means a
   bottle or vessel of skin. (Comp. 1 Sam. 1:24; 10:3; 25:18; 2
   Sam. 16:1, where the same Hebrew word is used.)