Source : Webster's Revised Unabridged Dictionary (1913)

Ponderous \Pon"der*ous\, a. [L. ponderosus, from pondus, -eris,
   a weight: cf. F. pond['e]reux. See {Ponder}.]
   1. Very heavy; weighty; as, a ponderous shield; a ponderous
      load; the ponderous elephant.

            The sepulcher . . . Hath oped his ponderous and
            marble jaws.                          --Shak.

   2. Important; momentous; forcible. ``Your more ponderous and
      settled project.'' --Shak.

   3. Heavy; dull; wanting; lightless or spirit; as, a ponderous
      style; a ponderous joke.

   {Ponderous spar} (Min.), heavy spar, or barytes. See
      {Barite}.

Source : WordNet®

ponderous
     adj 1: slow and laborious because of weight; "the heavy tread of
            tired troops"; "moved with a lumbering sag-bellied
            trot"; "ponderous prehistoric beasts"; "a ponderous
            yawn" [syn: {heavy}, {lumbering}]
     2: having great mass and weight and unwieldiness; "a ponderous
        stone"; "a ponderous burden"; "ponderous weapons"
     3: labored and dull; "a ponderous speech"