Disseisor
Encyclopedia
A Disseisor is the party in a case of adverse possession
Adverse possession
Adverse possession is a process by which premises can change ownership. It is a common law concept concerning the title to real property . By adverse possession, title to another's real property can be acquired without compensation, by holding the property in a manner that conflicts with the true...
who has taken actual possession of the property, thus "dis-seizing" (dispossessing) the true owner.
A Disseisee, the correlative, is the party put out of an estate, unlawfully.
http://onlinedictionary.datasegment.com/word/disseisee