night watch vs graveyard watch

night watch and graveyard watch both are nouns.

Word	Noun	Adjective	Verb	Adverb
night watch	Yes	No	No	No
graveyard watch	Yes	No	No	No

As nouns, night watch and graveyard watch are synonyms defined as:

night watch and graveyard watch: a watch during the night (as from midnight to 8 a.m.)

Other synonyms of night watch include middle watch, midwatch.

night watch (noun)	graveyard watch (noun)
a watch during the night (as from midnight to 8 a.m.)	a watch during the night (as from midnight to 8 a.m.)