The Collaborative International Dictionary of English v.0.48:

Disheritor \Dis*her"it*or\ (d[i^]s*h[e^]r"[i^]t*[~e]r), n. (Law)
   One who puts another out of his inheritance.
   [1913 Webster]

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

DISHERITOR. One who disinherits, or puts another out of his freehold.
Obsolete.