The Collaborative International Dictionary of English v.0.48:

Dumpy \Dump"y\, a. [Compar. Dumpier; superl. Dumpiest.] [
   1. From Dump a short ill-shapen piece.

   2. From Dump sadness.]

   1. Short and thick; of low stature and disproportionately
      stout.
      [1913 Webster]

   2. Sullen or discontented. See 2nd dump[1]. [Prov. Eng.]
      --Halliwell.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dumpy
    adj 1: resembling a garbage dump
    2: short and thick; as e.g. having short legs and heavy
       musculature; "some people seem born to be square and chunky";
       "a dumpy little dumpling of a woman"; "dachshunds are long
       lowset dogs with drooping ears"; "a little church with a
       squat tower"; "a squatty red smokestack"; "a stumpy ungainly
       figure" [syn: chunky, dumpy, low-set, squat,
       squatty, stumpy]
    3: short and plump [syn: dumpy, podgy, pudgy, tubby,
       roly-poly]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "dumpy":
   Lilliputian, Tom Thumb, adipose, beefy, big-bellied, bloated,
   blocky, blowzy, bosomy, brawny, burly, buxom, chubby, chunky,
   corpulent, distended, dwarf, dwarfed, dwarfish, elfin, fat,
   fattish, fleshy, formless, full, gross, heavyset, hefty, hippy,
   imposing, incipient, lusty, meager, meaty, midget, nanoid, obese,
   overweight, paunchy, plump, podgy, portly, potbellied, pudgy,
   puffy, pug, pugged, pursy, pygmy, retrousse, roly-poly, rotund,
   rudimental, rudimentary, runty, scraggy, scrubby, shapeless,
   shriveled, shrunk, shrunken, snub-nosed, square, squat, squattish,
   squatty, stalwart, stocky, stout, strapping, stubbed, stubby,
   stumpy, stunted, swollen, thick, thick-bodied, thickset, top-heavy,
   tubby, turned-up, undersize, undersized, unformed, well-fed,
   wizened