disapproval If you refer to something as a behemoth, you mean that it is extremely large, and often that it is is unpleasant, inefficient, or difficult to manage. The city is a sprawling behemoth with no heart. his behemoth 1,047 page book. = monster. an extremely large, mythical creature mentioned in the Bible, whose name is now used to describe something very big. something that is very large (Behemoth very large animal (probably a hippopotamus) mentioned in the Bible (14-21 centuries), from , from )