The Collaborative International Dictionary of English v.0.48:

Jujube \Ju"jube\ (j[=u]"j[-u]b), n. [F., fr. L. zizyphum, Gr.
   zi`zyfon, Per. z[imac]zf[=u]n, zizaf[=u]n, zayzaf[=u]n.]
   1. The sweet and edible drupes (fruits) of several
      Mediterranean and African species of small trees, of the
      genus Zizyphus, especially the Zizyphus jujuba,
      Zizyphus vulgaris, Zizyphus mucronata, and Zizyphus
      Lotus. The last named is thought to have furnished the
      lotus of the ancient Libyan Lotophagi, or lotus eaters.
      [1913 Webster]

   2. A chewy gelatinous lozenge made of or in imitation of, or
      flavored with, the jujube fruit.
      [Webster 1913 Suppl.]

   Jujube paste, the dried or inspissated jelly of the jujube;
      also, a confection made of gum arabic sweetened.
      [1913 Webster] Jiujutsu
      Jujitsu
      Jujutsu

The Collaborative International Dictionary of English v.0.48:

Christ's-thorn \Christ's-thorn`\, n. (Bot.)
   One of several prickly or thorny shrubs found in Palestine,
   especially the Paliurus aculeatus, Zizyphus
   Spina-Christi, and Zizyphus vulgaris. The last bears the
   fruit called jujube, and may be considered to have been the
   most readily obtainable for the Crown of Thorns.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jujube
    n 1: spiny tree having dark red edible fruits [syn: jujube,
         jujube bush, Christ's-thorn, Jerusalem thorn,
         Ziziphus jujuba]
    2: dark red plumlike fruit of Old World buckthorn trees [syn:
       jujube, Chinese date, Chinese jujube]
    3: chewy fruit-flavored jellied candy (sometimes medicated to
       soothe a sore throat)