American pit bull terrier

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A dog of a medium-sized to large breed developed in the United States from the Staffordshire bull terrier. Originally bred for fighting, it has a muscular body, broad head with powerful jaws, short coat, and black, blue, or red nose.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun American breed of muscular terriers with a short close-lying stiff coat