[1] : 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.
      1913 webster

            all sour things, as vinegar, provoke appetite.
                                                  --bacon.
      1913 webster

   2. changed, as by keeping, so as to be acid, rancid, or
      musty, turned.
      1913 webster

   3. disagreeable; unpleasant; hence; cross; crabbed; peevish;
      morose; as, a man of a sour temper; a sour reply. "a sour
      countenance." --swift.
      1913 webster

            he was a scholar . . .
            lofty and sour to them that loved him not,
            but to those men that sought him sweet as summer.
                                                  --shak.
      1913 webster

   4. afflictive; painful. "sour adversity." --shak.
      1913 webster

   5. cold and unproductive; as, sour land; a sour marsh.
      1913 webster

   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.
      1913 webster

   syn: acid; sharp; tart; acetous; acetose; harsh; acrimonious;
        crabbed; currish; peevish.
        1913 webster
see also:
sourer sourest sorrel sour dock sour gourd adansonia gregorii 
adansonia digitata adansonia sour grapes grape sour gum 
turelo sour plum owenia venosa 

[2] : The Collaborative International Dictionary of English v.0.48

tupelo \tu"pelo\, n. tupelo, or tupebo, the native american
   indian name. bot.
   a north american tree nyssa multiflora of the dogwood
   family, having brilliant, glossy foliage and acid red
   berries. the wood is crossgrained and very difficult to
   split. called also black gum, sour gum, and pepperidge.
   1913 webster

   largo tupelo, or tupelo gum bot., an american tree
      nyssa uniflora with softer wood than the tupelo.

   sour tupelo bot., the ogeechee lime.
      1913 webster
see also:
nyssa multiflora black gum sour gum pepperidge largo tupelo tupelo gum 
nyssa uniflora sour tupelo 

[3] : WordNet (r) 2.0

sour gum
     n : columnar tree of eastern north america having horizontal
         limbs and small leaves that emerge late in spring and
         have brilliant color in early fall syn: black gum, pepperidge,
          nyssa sylvatica
see also:
black gum pepperidge nyssa sylvatica 

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