unauthorized absence vs absence without leave

unauthorized absence and absence without leave both are nouns.

Word	Noun	Adjective	Verb	Adverb
unauthorized absence	Yes	No	No	No
absence without leave	Yes	No	No	No

As nouns, unauthorized absence and absence without leave are synonyms defined as:

unauthorized absence and absence without leave: unauthorized military absence

unauthorized absence (noun)	absence without leave (noun)
unauthorized military absence	unauthorized military absence