Real Dictionary

bulldog
countable noun: A bulldog is a small dog with a large square head and short hair.

bulldog in American English
a short-haired, square-jawed, heavily built dog noted for its strong stubborn grip
like or characteristic of a bulldog; stubborn, unrelenting, etc.
to throw (a steer) by taking hold of its horns and twisting its neck
adjective: like or characteristic of a bulldog or of a bulldog's jaws
noun: one of an English breed of medium-sized, short-haired, muscular dogs with prominent, undershot jaws, usually having a white and tan or brindled coat, raised originally for bullbaiting
transitive verb: to attack in the manner of a bulldog

bulldog in British English
noun: a sturdy thickset breed of dog with an undershot jaw, short nose, broad head, and a muscular body