sen·try 
/ˈsɛntri/ noun
plural sen·tries /ˈsɛntri/ noun [count] : a soldier who guards a door, gate, etc.
▪ The general placed/posted an armed sentry at the bridge. ▪ The company hired a policeman to stand sentry [=be a guard] by the door.
▪ The general placed/posted an armed sentry at the bridge. ▪ The company hired a policeman to stand sentry [=be a guard] by the door.
