Source : Webster's Revised Unabridged Dictionary (1913)

Sour \Sour\, a. [Compar. {Sourer}; superl. {Sourest}.] [OE.
   sour, sur, AS. s?r; akin to D. zuur, G. sauer, OHG. s?r,
   Icel. s?rr, Sw. sur, Dan. suur, Lith. suras salt, Russ.
   surovui harsh, rough. Cf. {Sorrel}, the plant.]
   1. Having an acid or sharp, biting taste, like vinegar, and
      the juices of most unripe fruits; acid; tart.

            All sour things, as vinegar, provoke appetite.
                                                  --Bacon.

   2. Changed, as by keeping, so as to be acid, rancid, or
      musty, turned.

   3. Disagreeable; unpleasant; hence; cross; crabbed; peevish;
      morose; as, a man of a sour temper; a sour reply. ``A sour
      countenance.'' --Swift.

            He was a scholar . . . Lofty and sour to them that
            loved him not, But to those men that sought him
            sweet as summer.                      --Shak.

   4. Afflictive; painful. ``Sour adversity.'' --Shak.

   5. Cold and unproductive; as, sour land; a sour marsh.

   {Sour dock} (Bot.), sorrel.

   {Sour gourd} (Bot.), the gourdlike fruit {Adansonia
      Gregorii}, and {A. digitata}; also, either of the trees
      bearing this fruit. See {Adansonia}.

   {Sour grapes}. See under {Grape}.

   {Sour gum} (Bot.) See {Turelo}.

   {Sour plum} (Bot.), the edible acid fruit of an Australian
      tree ({Owenia venosa}); also, the tree itself, which
      furnished a hard reddish wood used by wheelwrights.

   Syn: Acid; sharp; tart; acetous; acetose; harsh; acrimonious;
        crabbed; currish; peevish.

Source : WordNet®

sour dock
     n : European sorrel with large slightly acidic sagittate leaves
         grown throughout north temperate zone for salad and
         spring greens [syn: {garden sorrel}, {Rumex acetosa}]