Definition of "sentinel" in English

noun

1. A sentry, watch, or guard.

2. (obsolete) A private soldier.

3. (computer science) A unique value recognised by a computer program for processing in a special way, or marking the end of a set of data.

   • The <xmp> tag is a sentinel that suspends web-page processing and displays the subsequent text literally

4. A sentinel crab.

5. (attributive, medicine, epidemiology) A sign of a health risk (e.g. a disease, an adverse effect).

   • sentinel animals can be used to explore endemic diseases.

verb

1. (transitive) To watch over as a guard.

   • He sentineled the north wall.

2. (transitive) To post a guard for.

   • He sentineled the north wall with just one man.