D defs.my
Entry 2 senses Webster, 1913

Sentry

/sĕnʹtrē/ · Sen·try · IPA /ˈsɛn.tɹi/
01 n. A soldier placed on guard; a sentinel.
pl. Sentires ((#))
  1. 1.
    A soldier placed on guard; a sentinel.(Mil.)
  2. 2.
    Guard; watch, as by a sentinel.
    “Here toils, and death, and death's half-brother, sleep, Forms terrible to view, their sentry keep.” Dryden.
Phrases & compounds
Sentry box — a small house or box to cover a sentinel at his post, and shelter him from the weather.