The Collaborative International Dictionary of English v.0.48:

Intestacy \In*tes"ta*cy\, n. [From Intestate.]
   The state of being intestate, or of dying without having made
   a valid will. --Blackstone.
   [1913 Webster]

WordNet (r) 3.0 (2006):

intestacy
    n 1: the situation of being or dying without a legally valid
         will

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

INTESTACY. The state or condition of dying without a will.