A Sentry

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

Synonyms

• (nautical drag): kite