These words refer to weight or pressure so severe that it is difficult to bear. Heavy is the most informal and the least intense of these words indicating something of relative weightiness.

• He wondered if the floor could support the heavy piano; She insisted that the package was not very heavy .

Metaphorically, the word suggests something difficult or unpleasant: a heavy duty; He went to meet her with a heavy heart. The word need not, of course, suggest the idea of a carried weight at all. Burdensome , by contrast, specifically refers to something that is heavy and must be carried or supported; it is also more formal and more frequently used in an abstract way: a burdensome obligation; the burdensome post of chief administrator. The implication is that while the weight or task is difficult it can, with effort, be supported.

Onerous is thus an intensification of burdensome , being at the same time still more formal than the previous words. It is almost exclusively used abstractly for describing such things as supremely trying tasks or duties: the onerous job of correcting one hundred essays a week. The word gives an implication of an unfair or unjust assignment of duties: class assignments that were reasonable in one case and extremely onerous in another. Oppressive relates to this last possibility for onerous , suggesting harsh or cruel demands that can scarcely be borne: an oppressive taskmaster; oppressive taxation that reduced the peasants to a state of abject poverty. Crushing is the most intense of all these words and may suggest both literally and metaphorically, a weight or force that cannot be borne at all: the crushing impact of the plummeting airliner; poverty so crushing as to immobilize completely whole segments of society.