sentry: [17] Sentry is probably short for the now obsolete centrinell ‘sentry’. This first appeared in the 16th century as a variant of sentinel [16], which came via French sentinelle from Italian sentinella. It is not altogether clear where the Italian noun came from, but it may well have been derived from the verb sentire ‘perceive, watch’, a descendant of Latin sentīre ‘feel’ (from which English gets sense, sentence, sentiment, etc). => sentinel
sentry (n.)
1610s, originally "watchtower;" perhaps a shortened variant of sentinel, which had a variant form centrinel (1590s); or perhaps worn down from sanctuary, on notion of "shelter for a watchman." Meaning "military guard posted around a camp" is first attested 1630s. Sentry-box is from 1728.
