From The Collaborative International Dictionary of English v.0.48 [gcide]:
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.
[1913 Webster]
The sepulcher . . .
Hath oped his ponderous and marble jaws. --Shak.
[1913 Webster]
2. Important; momentous; forcible. "Your more ponderous and
settled project." --Shak.
[1913 Webster]
3. Heavy; dull; wanting; lightless or spirit; as, a ponderous
style; a ponderous joke.
[1913 Webster]
Ponderous spar (Min.), heavy spar, or barytes. See
Barite.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
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, ponderous]
2: having great mass and weight and unwieldiness; "a ponderous
stone"; "a ponderous burden"; "ponderous weapons"
3: labored and dull; "a ponderous speech"