sentinel vs sentry

sentinel and sentry both are nouns.

Word	Noun	Adjective	Verb	Adverb
sentinel	Yes	No	No	No
sentry	Yes	No	No	No

As nouns, sentinel and sentry are synonyms defined as:

sentinel and sentry: a person employed to keep watch for some anticipated event

Other synonyms of sentinel include lookout, lookout man, picket, scout, spotter, watch.

sentinel (noun)	sentry (noun)
a person employed to keep watch for some anticipated event	a person employed to keep watch for some anticipated event