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1.
A small-sized person or child with big-sized courage, heart and a bit scrappy. Loyal, he or she will stand up for his/her friends. Wlling to scrap with much larger opponents.
My five year-old picked a fight with the twleve-year old next door -- what a tiger-mouse!
by Jasper Ferg March 04, 2011
 
2.
1. A small or junior person with lots of heart, courage or moxy.

2. Small but scrappy, willing to take on anyone regardless of size.

From tiger + mouse
1. My six-year old tigermouse called 9-1-1 and stayed by his grandma's side until the medics arrived.

2. Little Billy's a tigermouse -- don't pick on him unless you want a bloody nose!
by JasperFerg October 04, 2011