Something is heavy which is denser and more compact in substance or larger in size or amount than the average of its kind or class and so weighs more in proportion.
In extended use what is heavy weighs down the senses or the spirits or is of such nature that the mind or the body finds difficult to bear or endure.
Often, also, heavy is applied to the heart, the mind, or the body to imply a being weighed down (as with grief, worry, weariness, or overwork).
At other times the term merely implies a lack of some quality (as lightness, vivacity, or grace) which enlivens and stimulates.
Something is weighty which is actually and not merely relatively heavy. In extended use what is weighty is highly important or momentous or produces a powerful effect or exerts an impressive influence.
Something is ponderous which is exceedingly heavy because of its size or its massiveness and cannot move or be moved quickly. In extended use what is ponderous is unduly intricate, involved, complicated, or labored.
Something is cumbrous or cumbersome which is so heavy and so bulky that it is difficult to deal with (as in moving or carrying). In extended use both words are applicable to what is both ponderous and unwieldy.
Something is hefty which one estimates as heavy or weighty (as by holding in one’s hands or by measuring with one’s eyes). In extended use the word may imply a generous amount or portion.