The Collaborative International Dictionary of English v.0.48:

Denization \Den`i*za"tion\, n.
   The act of making one a denizen or adopted citizen;
   naturalization. --Hallam.
   [1913 Webster]

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

DENIZATION, Eng. law.. The act by which a foreigner becomes a subject of
England; but he has not the rights either of a natural born subject, nor of
one who has become naturalized. Bac. Ab. Aliens, B.