Pronunciation: (sen'tn-l), [key]
—n., v., -neled, -nel•ing or (esp. Brit.) -nelled, -nel•ling.
1. a person or thing that watches or stands as if watching.
2. a soldier stationed as a guard to challenge all comers and prevent a surprise attack: to stand sentinel.
3. Also called tag. Computers.a symbol, mark, or other labeling device indicating the beginning or end of a unit of information.
to watch over or guard as a sentinel.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.