Merriam-Webster Collegiate Dictionary - imperial

 I. adjective  Etymology: Middle English, from Anglo-French, from Late Latin ~is, from Latin imperium command, empire  Date: 14th century  1.  a. of, relating to, befitting, or suggestive of an empire or an emperor  b.  (1) of or relating to the United Kingdom as distinguished from the constituent parts  (2) of or relating to the Commonwealth of Nations and British Empire  2.  a. sovereign  b. regal, imperious  3. of superior or unusual size or excellence  4. belonging to the official British series of weights and measures — see weight table  • ~ly adverb  II. noun  Date: circa 1524  1. capitalized an adherent or soldier of the Holy Roman emperor  2. emperor  3. French imperiale; from the beard worn by Napoleon III a pointed beard growing below the lower lip  4. something of unusual size or excellence