The Collaborative International Dictionary of English v.0.48:

Lancaster \Lancaster\ prop. n.
   1. A city in Northwest England on the river Lune. [WordNet
      sense 1]
      [WordNet 1.5]

   2. The English royal house that reigned from 1399 to 1461;
      its symbol was a red rose; called also the House of
      Lancaster. [WordNet sense 2]

   Syn: Lancastrian line.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

House of Lancaster
    n 1: the English royal house that reigned from 1399 to 1461; its
         emblem was a red rose [syn: Lancaster, House of
         Lancaster, Lancastrian line]