Source : Webster's Revised Unabridged Dictionary (1913)

Weighty \Weight"y\, a. [Compar. {Weightier}; superl.
   {Weightiest}.]
   1. Having weight; heavy; ponderous; as, a weighty body.

   2. Adapted to turn the balance in the mind, or to convince;
      important; forcible; serious; momentous. ``For sundry
      weighty reasons.'' --Shak.

            Let me have your advice in a weighty affair.
                                                  --Swift.

   3. Rigorous; severe; afflictive. [R.] ``Attend our weightier
      judgment.'' --Shak.

   Syn: Heavy; ponderous; burdensome; onerous; forcible;
        momentous; efficacious; impressive; cogent.

Source : WordNet®

weighty
     adj 1: having relatively great weight; heavy; "a weighty load"; "a
            weighty package" [ant: {weightless}]
     2: of great gravity or crucial import; requiring serious
        thought; "grave responsibilities"; "faced a grave decision
        in a time of crisis"; "a grievous fault"; "heavy matters
        of state"; "the weighty matters to be discussed at the
        peace conference" [syn: {grave}, {grievous}, {heavy}]
     3: weighing heavily on the spirit; causing anxiety or worry;
        "weighty problems"
     4: excessively fat; "a weighty man" [syn: {corpulent}, {obese},
         {rotund}]
     5: powerfully persuasive; "a cogent argument"; "a telling
        presentation"; "a weighty argument" [syn: {cogent}, {telling}]
     [also: {weightiest}, {weightier}]

weightiest
     See {weighty}