weighty

adj. heavy, grave, serious; oppressive, burdensome; carrying a lot of weight; very significant, highly influential

In the physical sciences, weight is a measurement of the gravitational force acting on an object. Near the surface of the Earth, the acceleration due to gravity is approximately constant; this means that an object's weight is roughly proportional to its mass. The words "weight" and "mass" are therefore often used interchangeably, even though they do not describe the same concept. Weight is the force with which a body is attracted toward the earth or a celestial body by gravitation and which is equal to the product of the mass and the local gravitational acceleration
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Adjective
1. having relatively great weight; heavy; "a weighty load"; "a weighty package"
(antonym) 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"
(synonym) grave, grievous, heavy
(similar) important, of import
3. weighing heavily on the spirit; causing anxiety or worry; "weighty problems"
(similar) heavy
4. excessively fat; "a weighty man"
(synonym) corpulent, obese, rotund
(similar) fat
5. powerfully persuasive; "a cogent argument"; "a telling presentation"; "a weighty argument"
(synonym) cogent, telling
(similar) forceful

(superl.)
Rigorous; severe; afflictive.
  

(superl.)
Having weight; heavy; ponderous; as, a weighty body.
  

(superl.)
Adapted to turn the balance in the mind, or to convince; important; forcible; serious; momentous.
  

loading; weighty
  

heavy; weighty