sentry duty vs duty assignment

sentry duty and duty assignment both are nouns.

Word	Noun	Adjective	Verb	Adverb
sentry duty	Yes	No	No	No
duty assignment	Yes	No	No	No

As nouns, duty assignment is a hypernym of sentry duty; that is, duty assignment is a word with a broader meaning than sentry duty:

sentry duty: the duty of serving as a sentry
duty assignment: a duty that you are assigned to perform (especially in the armed forces)

Other hypernyms of sentry duty include assignment.

sentry duty (noun)	duty assignment (noun)
the duty of serving as a sentry	a duty that you are assigned to perform (especially in the armed forces)