sentry vs sentinel

sentry and sentinel both are nouns.

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

As nouns, sentry and sentinel are synonyms defined as:

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

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

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