The Collaborative International Dictionary of English v.0.48:

Possessory \Pos*sess"o*ry\, a. [L. possessorius: cf. F.
   possessoire.]
   Of or pertaining to possession, either as a fact or a right;
   of the nature of possession; as, a possessory interest; a
   possessory lord.
   [1913 Webster]

   Possessory action or Possessory suit (Law), an action to
      regain or obtain possession of something. See under
      Petitory.
      [1913 Webster]

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

POSSESSORY ACTION, old Eng. law. A real action in which the plaintiff called
the demandant, sought to recover the possession of lands, tenements, and
hereditaments. On account of the great nicety required in its management,
and the introduction of more expeditious methods of trying titles by other
actions, it has been laid aside. Finch's Laws, 257; 3 Bouv. Inst. n. 2640.
     2. In Louisiana, by this term is understood an action by which one
claims to be maintained in the possession of an immovable property, or of a
right upon or growing out of it, when he has been disturbed: or to be
reinstated to that possession, when he has been divested or evicted. Code of
Practice, art. 6; 2 L. R. 227, 454.