Source : Webster's Revised Unabridged Dictionary (1913)

Sorrel \Sor"rel\, n. [F. surelle, fr. sur sour, fr. OHG. s?r
   sour. See {Sour}.] (Bot.)
   One of various plants having a sour juice; especially, a
   plant of the genus {Rumex}, as {Rumex Acetosa}, {Rumex
   Acetosella}, etc.

   {Mountain sorrel}. (Bot.) See under {Mountain}.

   {Red sorrel}. (Bot.)
   (a) A malvaceous plant ({Hibiscus Sabdariffa}) whose acid
       calyxes and capsules are used in the West Indies for
       making tarts and acid drinks.
   (b) A troublesome weed ({Rumex Acetosella}), also called
       {sheep sorrel}.

   {Salt of sorrel} (Chem.), binoxalate of potassa; -- so called
      because obtained from the juice of {Rumex Acetosella}, or
      {Rumex Axetosa}.

   {Sorrel tree} (Bot.), a small ericaceous tree ({Oxydendrum
      arboreum}) whose leaves resemble those of the peach and
      have a sour taste. It is common along the Alleghanies.
      Called also {sourwood}.

   {Wood sorrel} (Bot.), any plant of the genus Oxalis.

Source : WordNet®

sorrel tree
     n 1: deciduous shrubby tree of eastern North America having
          deeply fissured bark and sprays of small fragrant white
          flowers and sour-tasting leaves [syn: {sourwood}, {titi},
           {Oxydendrum arboreum}]
     2: Australian tree with acid foliage [syn: {Hibiscus
        heterophyllus}]