Definition from Wiktionary, the free dictionary
a. 1971, from a riddle: "Where does an 800-pound gorilla sleep?" / "Anywhere it wants."
- (idiomatic) An entity that dominates its environment.
- (idiomatic) Something dangerous, menacing, or spooky that is obvious but not addressed.
- The weight in the metaphor can be varied quantitatively.
- Occasionally other nouns are substituted, most commonly elephant from another idiom, but also more context-specific nouns, such as rutabaga in an article on gardening.
- Occasionally adjectives are inserted to modify gorilla to bring the metaphor closer to the context.
- 800-pound gorilla at OneLook Dictionary Search