The Collaborative International Dictionary of English v.0.48:

Ownership \Own"er*ship\, n.
   The state of being an owner; the right to own; exclusive
   right of possession; legal or just claim or title;
   proprietorship.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ownership
    n 1: the relation of an owner to the thing possessed; possession
         with the right to transfer possession to others
    2: the act of having and controlling property [syn:
       possession, ownership]
    3: the state or fact of being an owner