sentinel
/ˈsɛn.tɪ.nəl/ noun C2- A sentry, watch, or guard.
- 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
- A sentinel crab.
- A sign of a health risk (e.g. a disease, an adverse effect). · Sentinel animals can be used to explore endemic diseases.
Plural sentinels
From the library
He looked around; he was in a court surrounded by high walls; he heard the measured tread of sentinels, and as they passed before the light he saw the barrels of their muskets shine.
To undermine the ground for fifty feet—to devote three years to a labor which, if successful, would conduct you to a precipice overhanging the sea—to plunge into the waves from the height of fifty, sixty, perhaps a hundred feet, at the risk of being dashed to pieces against the rocks, should you have been fortunate enough to have escaped the fire of the sentinels; and even, supposing all these perils past, then to have to swim for your life a distance of at least three miles ere you could reach the shore—were difficulties so startling and formidable that Dantès had never even dreamed of such a scheme, resigning himself rather to death.
This time you will lay your plans more accurately; we shall get out into the gallery you have described; kill the sentinel who guards it, and make our escape.
“Ah, if there were no sentinel!”
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