The Collaborative International Dictionary of English v.0.48:

Proprietor \Pro*pri"e*tor\, n. [For older proprietary: cf. F.
   propri['e]tarie.]
   One who has the legal right or exclusive title to anything,
   whether in possession or not; an owner; as, the proprietor of
   farm or of a mill.
   [1913 Webster]

WordNet (r) 3.0 (2006):

proprietor
    n 1: (law) someone who owns (is legal possessor of) a business;
         "he is the owner of a chain of restaurants" [syn: owner,
         proprietor]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "proprietor":
   beneficiary, cestui, cestui que trust, cestui que use, deedholder,
   feoffee, feudatory, holder, householder, innkeeper, laird,
   landholder, landlady, landlord, landowner, licensee, lord, manager,
   master, mesne, mesne lord, mistress, owner, partner, possessor,
   property owner, proprietary, proprietress, proprietrix, publican,
   rentier, squire, titleholder



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PROPRIETOR. The owner. (q.v.)