Definition of "sentry" [sen•try]

• A guard, especially a soldier posted at a given spot to prevent the passage of unauthorized persons. (noun)
• The duty of a sentry; watch. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "It was pitch dark, so I called the sentry and told him some one was hurt."
• "In a loud voice he called the sentry who was pacing below; and in a moment the man appeared in answer to that summons."
• ""There he go back and forrards, doing what he call his sentry go."