In law, an individual who has died.
Synomous with "the deceased".
For a sample of the word used in Canadian statute, consider ¶616 of Quebec's Civil Code:
"Where persons die and it is impossible to determine which survived the other, they are deemed to have died at the same time if at least one of them is called to the succession of the other. The succession of each of the decedents then devolves to the persons who would have been called to take it in his place."
The word is in great use in the United States to formally refer to the deceased in estate administration statutes such as intestacy laws. For example, the 2005 model or proposed uniform probate code of the United States, ¶2-104, contains this provision (published at law.upenn.edu/bll/archives/ulc/upc/final2005.htm):
"An individual who fails to survive the decedent by 120 hours is deemed to have predeceased the decedent for purposes of homestead allowance, exempt property, and intestate succession, and the decedent's heirs are determined accordingly...."