The Collaborative International Dictionary of English v.0.48:

Jar \Jar\ (j[aum]r), n. [F. jarre, Sp. jarra, from Ar. jarrah
   ewer; cf. Pers. jarrah.]
   1. A deep, broad-mouthed vessel of earthenware or glass, for
      holding fruit, preserves, etc., or for ornamental
      purposes; as, a jar of honey; a rose jar. --Dryden.
      [1913 Webster]

   2. The measure of what is contained in a jar; as, a jar of
      oil; a jar of preserves.
      [1913 Webster]

   Bell jar, Leyden jar. See in the Vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Leyden jar \Ley"den jar"\ (l[imac]"d'n j[aum]r"; 277) Leyden
phial \Ley"den phi"al\ (f[imac]"al).n. (Elec.)
   A glass jar or bottle used to accumulate electricity. It is
   coated with tin foil, within and without, nearly to its top,
   and is surmounted by a brass knob which communicates with the
   inner coating, for the purpose of charging it with
   electricity. It is so named from having been invented in
   Leyden, Holland.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Leyden jar
    n 1: an electrostatic capacitor of historical interest [syn:
         Leiden jar, Leyden jar]