anyone or anything small or undersized. can also mean timid weak or being a pussy.
i've caught several fish in this lake but they are all milli-mouths. stop being a fucking milli-mouth and beat that guy's ass!
by tomscrews September 09, 2008
small in stature, timid, scared of confrontation. an all around pussy.
1. I've caught fish in this lake before but they are all milli's or milli-mouths. 2. Don't be such a milli-mouth and whip his ass. 3. That guy is a milli-mouth maggot!
by Thomas Crews August 30, 2008