sentinel

1570s, from Middle French sentinelle, from Old Italian sentinella (perhaps via a notion of "perceive, watch", compare Italian sentire (“to feel, hear, smell”)), from Latin sentiō (“feel, perceive by the senses”). See sense.

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sentinel (plural sentinels)

1. A sentry or guard.
   • 1719- Daniel Defoe, Robinson Crusoe

     They promised faithfully to bear their confinement with patience, and were very thankful that they had such good usage as to have provisions and light left them; for Friday gave them candles (such as we made ourselves) for their comfort; and they did not know but that he stood sentinel over them at the entrance.

   • Macaulay

     the sentinels who paced the ramparts

2. (computer science) a unique string of characters recognised by a computer program for processing in a special way; a keyword.

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

3. Watch; guard.
   • Francis Bacon

     that princes do keep due sentinel

4. A sentinel crab.

sentinel (third-person singular simple present sentinels, present participle (US) sentineling or (UK) sentinelling, simple past and past participle (US) sentineled or (UK) sentinelled)

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

   He sentineled the north wall.

2. (transitive) To post as guard.

   He sentineled him on the north wall.

3. (transitive) To post a guard for.

   He sentineled the north wall with just one man.

• lenients