backupsentry
nounUK /ˈbækʌpˌsɛntri/
US /ˈbækʌpˌsɛntri/
A backup sentry is a helper guard who watches over a place when the main guard needs a rest.
The backup sentry stood by the gate while the first guard took a break.
OTHER MEANINGS
2. A second guard who steps in if the first one cannot do the job.
When the main sentry got sick, the backup sentry took over the night watch.
3. A person or thing that gives extra protection to a team or place.
The coach kept a backup sentry on the bench in case the goalie got hurt.
4. A spare guard used during busy or dangerous times.
They called in a backup sentry during the big festival.