The Collaborative International Dictionary of English v.0.48:

Spongy \Spon"gy\ (sp[u^]n"j[y^]), a.
   1. Soft, and full of cavities; of an open, loose, pliable
      texture; as, a spongy excrescence; spongy earth; spongy
      cake; spongy bones.
      [1913 Webster]

   2. Wet; drenched; soaked and soft, like sponge; rainy.
      "Spongy April." --Shak.
      [1913 Webster]

   3. Having the quality of imbibing fluids, like a sponge.
      [1913 Webster]

   Spongy lead (Chem.), sponge lead. See under Sponge.

   Spongy platinum. See under Platinum.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spongy
    adj 1: easily squashed; resembling a sponge in having soft
           porous texture and compressibility; "spongy bread" [syn:
           spongy, squashy, squishy, spongelike]
    2: like a sponge in being able to absorb liquids and yield it
       back when compressed [syn: spongy, spongelike]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "spongy":
   absorbent, adsorbent, assimilative, baccate, bibulous, blotting,
   chemisorptive, chemosorptive, cribriform, digestive, doughy,
   edematous, endosmotic, exosmotic, flabby, fleshy, imbibitory,
   leachy, macerated, masticated, medullary, mushy, osmotic, pappy,
   pasty, percolating, pithy, porose, porous, pulpal, pulpar, pulped,
   pulplike, pulpy, puppy, quaggy, resorbent, sievelike, soaking,
   soft, sorbent, spongelike, spongeous, squashy, squelchy, squishy,
   succulent, thirsty, yielding