postmortal vs postmortem

postmortal is not a noun while postmortem is a noun.

Word	Noun	Adjective	Verb	Adverb
postmortal	No	Yes	No	No
postmortem	Yes	Yes	No	No

As adjectives, postmortal and postmortem are synonyms defined as:

postmortal (noun)	postmortem (noun)
	an examination and dissection of a dead body to determine cause of death or the changes produced by disease
	discussion of an event after it has occurred

postmortal (adjective)	postmortem (adjective)
occurring or done after death	occurring or done after death
	after death or after an event