sentinels

noun

1. 1

   A sentry, watch, or guard.

2. 2

   A private soldier.

3. 3

   A unique string of characters recognised by a computer program for processing in a special way; a keyword.

   “The tag is a sentinel that suspends web-page processing and displays the subsequent text literally.”

4. 4

   A sentinel crab.

5. 5

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

   “sentinel animals can be used to explore endemic diseases.”