Adjective
The word is derived from weighty
Man must not only make himself: the weightiest thing he has to do is to determine what he is going to be. He is causa sui to the second power. José Ortega y Gasset
In the weightiest matters we must go to school to the animals, and learn spinning and weaving from the spider, building from the swallow, singing from the birds,-from the swan and the nightingale, imitating their art. Democritus
The weightiest end of the cross of Christ that is laid upon you, lieth upon your strong Savior. Samuel Rutherford