The Collaborative International Dictionary of English v.0.48:

Bladder \Blad"der\ (bl[a^]d"d[~e]r), n. [OE. bladder, bleddre,
   AS. bl[=ae]dre, bl[=ae]ddre; akin to Icel. bla[eth]ra, SW.
   bl[aum]ddra, Dan. bl[ae]re, D. blaar, OHG. bl[=a]tara the
   bladder in the body of animals, G. blatter blister, bustule;
   all fr. the same root as AS. bl[=a]wan, E. blow, to puff. See
   Blow to puff.]
   [1913 Webster]
   1. (Anat.) A bag or sac in animals, which serves as the
      receptacle of some fluid; as, the urinary bladder; the
      gall bladder; -- applied especially to the urinary
      bladder, either within the animal, or when taken out and
      inflated with air.
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   2. Any vesicle or blister, especially if filled with air, or
      a thin, watery fluid.
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   3. (Bot.) A distended, membranaceous pericarp.
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   4. Anything inflated, empty, or unsound. "To swim with
      bladders of philosophy." --Rochester.
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   Bladder nut, or Bladder tree (Bot.), a genus of plants
      (Staphylea) with bladderlike seed pods.

   Bladder pod (Bot.), a genus of low herbs (Vesicaria) with
      inflated seed pods.

   Bladdor senna (Bot.), a genus of shrubs (Colutea), with
      membranaceous, inflated pods.

   Bladder worm (Zool.), the larva of any species of tapeworm
      (T[ae]nia), found in the flesh or other parts of
      animals. See Measle, Cysticercus.

   Bladder wrack (Bot.), the common black rock weed of the
      seacoast (Fucus nodosus and Fucus vesiculosus) --
      called also bladder tangle. See Wrack.
      [1913 Webster]