postmortem vs postmortal

postmortem is a noun but postmortal is not a noun.

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

As adjectives, postmortem and postmortal are synonyms defined as:

postmortem (noun)	postmortal (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

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