any person who talks non-stop and quite fast, esp. about inconsequential topics; also, the incessant chatter of this type of person
The 11-year-old is a motormouth about Pokemon.
: I didn't know he was motor-mouth/ The gangsta rapper is wrecking the mike with motormouth rhymes
A very talkative person; a compulsive jabberer; flapjaw, windbag: What else can you do with this motor-mouth but grin and bear it?/ He keeps on talking. A motor-mouth, this guy (1971+)