Bulldog

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

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.