MUMBLE interj. 1. Said when the correct response is either too complicated to enunciate or the speaker has not thought it out. Often prefaces a longer answer, or indicates a general reluctance to get into a big long discussion. "Well, mumble." 2. Sometimes used as an expression of disagreement. "I think we should buy it." "Mumble!" Common variant: MUMBLE FROTZ. 3. Yet another metasyntactic variable, like FOO.