1. To promote or aggrandize the importance, quality, or positive aspects of someone or something. The promoters have really been bigging up this new band; I hope their concert is as good as we've been led to believe. First impressions are really important, so I'd like it if you could big me up to your boss before I meet her.

2. To make one's body larger and/or more muscular, as by weight-training exercises. I was always a really skinny kid, so I got this gym membership so I could really big up.