1. silence directed toward paltry affairs of this world and universe
2. wordless response to anything common, ordinary, banal or totally unimaginative
1. When Bubba and the harem were on a roll cavorting and carrying on Carey raised his eyebrows and put on his best mumdane grin.
2. Any time Uncle Sammy came up with one of his new get rich quick schemes (apart from milking addicted divorced women) the whole gang and family would exhibit their best mumdane looks and eyebrow wiggles.