The Collaborative International Dictionary of English v.0.48:

Hyssop \Hys"sop\, n. [OE. hysope, ysope, OF. ysope, F. hysope,
   hyssope, L. hysopum, hyssopum, hyssopus, Gr. ?, ?, an
   aromatic plant, fr. Heb. [=e]sov.]
   A plant (Hyssopus officinalis). The leaves have an aromatic
   smell, and a warm, pungent taste.
   [1913 Webster]

   Note: The hyssop of Scripture is supposed to be a species of
         caper (Capparis spinosa), but probably the name was
         used for several different plants.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Caper \Ca"per\, n. [F. c[^a]pre, fr. L. capparis, Gr. ?; cf. Ar.
   & Per. al-kabar.]
   1. The pungent grayish green flower bud of the European and
      Oriental caper (Capparis spinosa), much used for
      pickles.
      [1913 Webster]

   2. (Bot.) A plant of the genus Capparis; -- called also
      caper bush, caper tree.
      [1913 Webster]

   Note: The Capparis spinosa is a low prickly shrub of the
         Mediterranean coasts, with trailing branches and
         brilliant flowers; -- cultivated in the south of Europe
         for its buds. The Capparis sodada is an almost
         leafless spiny shrub of central Africa (Soudan),
         Arabia, and southern India, with edible berries.
         [1913 Webster]

   Bean caper. See Bran caper, in the Vocabulary.

   Caper sauce, a kind of sauce or catchup made of capers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Capparis spinosa
    n 1: prostrate spiny shrub of the Mediterranean region
         cultivated for its greenish flower buds which are pickled
         [syn: common caper, Capparis spinosa]