any of a breed of very large, reddish-brown and white dog once kept by the monks of the hospice of the Great St. Bernard Pass in the Swiss Alps, and trained to rescue travelers lost in the snow: now kept as a companion dog
See Saint Bernard in American Heritage Dictionary 4
noun
Any of a breed of large strong dog developed in Switzerland, having a thick brown and white coat, originally used by monks of the hospice of Saint Bernard in the Swiss Alps to help patrol the snow-covered region.