Etymology
Advertisement

sentry (n.)

1610s, "a defensive military watchtower;" perhaps a shortened variant of sentinel, which had a variant form centrinel (1590s); or perhaps it is from sentry, a 16c. worn-down form of sanctuary (n.), on the notion of "shelter for a watchman." The meaning "military guard posted around a camp" is attested by 1630s. Sentry-box, "booth to give shelter to a sentry in bad weather," is from 1728.

Advertisement
Advertisement
Definitions of sentry

sentry (n.)
a person employed to keep watch for some anticipated event;
Synonyms: lookout / lookout man / sentinel / watch / spotter / scout / picket
From wordnet.princeton.edu