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]