The Collaborative International Dictionary of English v.0.48:

disherison \dis*her"i*son\ (d[i^]s*h[e^]r"[i^]z'n), n. [See
   Disherit.]
   The act of disheriting, or debarring from inheritance;
   disinherison. --Bp. Hall.
   [1913 Webster]

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

DISHERISON. Disinheritance; depriving one of an inheritance. Obsolete. Vide
Disinherison.