Pertaining to something that is extremely large and overwhelming: Monroe made a behemothian blunder when he quit his job; especially, since he could not find another one nearly as good as the one he left.

There is a popular notion that behemothian dinosaurs were so ponderous and lumbering that their great hulks and weights prevented them from roaming very far from where they were born.

A behemothian corporation is a very large business company or organization.