·adj Characteristic of, or like, a bulldog; stubborn; as, bulldog courage; bulldog tenacity.
II. Bulldog ·noun A refractory material used as a furnace lining, obtained by calcining the cinder or slag from the puddling furnace of a rolling mill.
III. Bulldog ·noun A variety of dog, of remarkable ferocity, courage, and tenacity of grip;
— so named, probably, from being formerly employed in baiting bulls.