Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
ponderous [ˈpɔndərəs] adj (style) тяжелове́сный*тяжелове́сен (person) неповоро́тливый/неповоро́тлив
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.