The Collaborative International Dictionary of English v.0.48:

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.
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            All sour things, as vinegar, provoke appetite.
                                                  --Bacon.
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   2. Changed, as by keeping, so as to be acid, rancid, or
      musty, turned.
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   3. Disagreeable; unpleasant; hence; cross; crabbed; peevish;
      morose; as, a man of a sour temper; a sour reply. "A sour
      countenance." --Swift.
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            He was a scholar . . .
            Lofty and sour to them that loved him not,
            But to those men that sought him sweet as summer.
                                                  --Shak.
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   4. Afflictive; painful. "Sour adversity." --Shak.
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   5. Cold and unproductive; as, sour land; a sour marsh.
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   Sour dock (Bot.), sorrel.

   Sour gourd (Bot.), the gourdlike fruit Adansonia
      Gregorii, and Adansonia 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.
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   Syn: Acid; sharp; tart; acetous; acetose; harsh; acrimonious;
        crabbed; currish; peevish.
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The Collaborative International Dictionary of English v.0.48:

Adansonia \Ad`an*so"ni*a\, n. [From Adanson, a French botanist.]
   (Bot.)
   A genus of great trees related to the Bombax. There are two
   species, Adansonia digitata, the baobab or monkey-bread of
   Africa and India, and Adansonia Gregorii, the sour gourd or
   cream-of-tartar tree of Australia. Both have a trunk of
   moderate height, but of enormous diameter, and a
   wide-spreading head. The fruit is oblong, and filled with
   pleasantly acid pulp. The wood is very soft, and the bark is
   used by the natives for making ropes and cloth. --D. C.
   Eaton.
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WordNet (r) 3.0 (2006):

Adansonia gregorii
    n 1: Australian tree having an agreeably acid fruit that
         resembles a gourd [syn: cream-of-tartar tree, sour
         gourd, Adansonia gregorii]