sentry

noun

Etymology: From earlier sentrie, sentery, of uncertain origin. Perhaps an alteration of sentinel or sanctuary; or perhaps from Old French senteret (“a path”), diminutive of sentier, from Medieval Latin semitarius (“a path”).

1. A guard, particularly on duty at the entrance to a military base.

   “Additional sentries are keeping watch for any signs of an ambush.”

2. Sentry duty; time spent being a sentry.
3. A form of drag to be towed underwater, which on striking bottom is upset and rises to the surface.
4. A watchtower.
5. An animal like a marmot tasked with alerting the pack to danger.