An almost-synonym for broner. The difference between a chumby and a full-on broner is the degree of erection. See chubby and boner for more detail. If definition is still not understood, see pun.
Maerri: "Hey chumbies, check this out - when you sing in the chumby, your acousticsreverberate throughout the chumby and it's keeping me awake which makes me feel real chumby. Would you mind keeping it chumby?"
Culver: "Whoah, put your chumby on a leash."