1. noun The heaviest weight class of boxers. A: "In professional boxing, how much does a heavyweight actually have to weigh?" B: "More than 175 pounds."

2. noun, slang A very important person. I'm not a heavyweight on those kinds of issues—you should really ask Stewart about it.

3. adjective Participating in the heaviest weight-class of boxers. A: "How much does a professional heavyweight boxer actually have to weigh?" B: "More than 175 pounds."

4. adjective, slang Very important. I'm not a heavyweight person on those kinds of issues, so you should really ask your boss about it.