You can call both a Tyrannosaurus Rex and a massive telecommunications company a behemoth. The word means something big and powerful.
Behemoth comes from the Hebrew word b'hemah meaning beast. You can use it to describe large animals or large entities that make you feel small and powerless when you have to confront them. If a behemoth of a moose charges your car, you deal with it, and then with a behemoth of an insurance company, where just finding who to talk to is nearly impossible.