The Collaborative International Dictionary of English v.0.48:

Possessor \Pos*sess"or\, n. [L.: cf. F. possesseur.]
   One who possesses; one who occupies, holds, owns, or
   controls; one who has actual participation or enjoyment,
   generally of that which is desirable; a proprietor.
   "Possessors of eternal glory." --Law.
   [1913 Webster]

         As if he had been possessor of the whole world.
                                                  --Sharp.
   [1913 Webster]

   Syn: Owner; proprietor; master; holder; occupant.
        [1913 Webster]

WordNet (r) 3.0 (2006):

possessor
    n 1: a person who owns something; "they are searching for the
         owner of the car"; "who is the owner of that friendly
         smile?" [syn: owner, possessor]

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

POSSESSOR. He who holds, detains or enjoys a thing, either by himself or his
agent, which he claims as his own.
     2. In general the possessor of personal chattels is presumed to be the
owner; and in case of real estate he has a right to receive the profits,
until a title adverse to his possession has been established, leaving him
subject to an action for the mesne profits. (q.v.)