The Collaborative International Dictionary of English v.0.48:

Decedent \De*ce"dent\, a. [L. decedens, p. pr. of decedere.]
   Removing; departing. --Ash.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decedent \De*ce"dent\, n.
   A deceased person. --Bouvier.
   [1913 Webster]

WordNet (r) 3.0 (2006):

decedent
    n 1: someone who is no longer alive; "I wonder what the dead
         person would have done" [syn: dead person, dead soul,
         deceased person, deceased, decedent, departed]

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

DECEDENT. In the acts of descent and distribution in Pennsylvania, this word
is frequently used for a deceased person, testate or intestate.