absence without leave vs unauthorized absence

absence without leave and unauthorized absence both are nouns.

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

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

absence without leave and unauthorized absence: unauthorized military absence

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