sen·try / ˈsentrē/ • n. (pl. -tries) a soldier stationed to keep guard or to control access to a place.PHRASES: stand sentry keep guard or control access to a place.

sentry †sentinel; armed member of the fighting forces set to keep guard. XVII. perh. shortening of †centrinell, -onel (XVI), vars. of SENTINEL, with assim. to -RY. comp. sentry-go, †orig. phr. consisting of sentry sb. (used vocatively) and imper. of Go; (hence) patrol or duties of a s. XIX.