The Collaborative International Dictionary of English v.0.48:
Porterhouse \Por"ter*house\, n. A house where porter is sold. [1913 Webster] Porterhouse steak, a steak cut from a sirloin of beet, including the upper and under part. [1913 Webster]WordNet (r) 3.0 (2006):
porterhouse n 1: large steak from the thick end of the short loin containing a T-shaped bone and large piece of tenderloin [syn: porterhouse, porterhouse steak]