sentry go vs guard duty

sentry go and guard duty both are nouns.

Word	Noun	Adjective	Verb	Adverb
sentry go	Yes	No	No	No
guard duty	Yes	No	No	No

As nouns, sentry go and guard duty are synonyms defined as:

Other synonyms of sentry go include guard, sentry duty.

sentry go (noun)	guard duty (noun)
the duty of serving as a sentry	the duty of serving as a sentry