noun, verb, -neled, -nel⋅ing or (especially British
) -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. |
| 4. | to watch over or guard as a sentinel. |
