The Collaborative International Dictionary of English v.0.48:

Demijohn \Dem"i*john\, n. [F. dame-jeanne, i.e., Lady Jane, a
   corruption of Ar. damaj[=a]na, damj[=a]na, prob. fr. Damaghan
   a town in the Persian province of Khorassan, once famous for
   its glass works.]
   A glass vessel or bottle with a large body and small neck,
   inclosed in wickerwork.
   [1913 Webster]

WordNet (r) 3.0 (2006):

demijohn
    n 1: large bottle with a short narrow neck; often has small
         handles at neck and is enclosed in wickerwork