sentry

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”).

noun

1. A guard, particularly on duty at the entrance to a military base.
   Additional sentries are keeping watch for any signs of an ambush. 2019, Maaza Mengiste, The Shadow King, Canongate Books (2020), page 213
2. (uncountable) Sentry duty; time spent being a sentry.
3. (nautical) A form of drag to be towed underwater, which on striking bottom is upset and rises to the surface.
4. A watchtower.
5. A animal like a marmot tasked with alerting the pack to danger.