1. The having of pre-pubescent facial hair above the lip.
2. A human of the female variety with a hairy upper lip.
3. The act of being a complete and utter hairy douchebag.
4. The act of gluing your partner's lips shut with your cum.
Ted:OMG! Todd,what the fuck is that on Mary's face?
Todd: I think it's a damn masteusche!
Grisly: "Grow some balls and shave that masteusche, nigger boy neal"
Captain America: "Wonder Boy, the next time I see your mom, I'm going to masteusche her lips together."