big up verb 4noun 1forms 5 verb4 •(informal) To increase one's muscle mass.She was bigged up—had a weight-lifter's rippling arms. — 2007 •(slang) To proclaim or exaggerate the importance of; to promote.I want to big up my bro on the mic.They're trying to big themselves up to be more than they are. •(informal) To become big. •(slang) To behave confidently and proudly. noun1 •(slang) Significant respect or acclaim.I want to give a big up to my bro on the mic. formsbig upped · bigged up · bigging up · bigs up · big ups