sentinel
Americannoun
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sentinels
plural
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a person or thing that watches or stands as if watching.
The cats were the sentinels of the house, patrolling constantly for rodents, dogs, and other invaders.
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a soldier stationed as a guard to challenge all comers and prevent a surprise attack.
Lincoln refused to make his home mansion a garrison during the Civil War, but plain-clothes sentinels did patrol the property
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Digital Technology. tag.
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Medicine/Medical. an indication or mark that a disease is present or prevalent.
New viruses in the wastewater can be used as sentinels of future outbreaks.
verb (used with object)
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sentinels,
present (3rd person singular)
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sentineled,
past participle, past
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sentinelled,
past participle, past (especially British)
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sentineling,
present participle
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sentinelling
present participle (especially British)
adjective
noun
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a person, such as a sentry, assigned to keep guard
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computing a character used to indicate the beginning or end of a particular block of information
verb
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to guard as a sentinel
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to post as a sentinel
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to provide with a sentinel
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Participles
Conjugated Forms
Present
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sentinelsimple
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sentinelssimple
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have sentineledperfect
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have sentinelledperfect
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has sentineledperfect
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has sentinelledperfect
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am sentinelingprogressive
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am sentinellingprogressive
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are sentinelingprogressive
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are sentinellingprogressive
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is sentinelingprogressive
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is sentinellingprogressive
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have been sentinelingperfect progressive
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have been sentinellingperfect progressive
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has been sentinelingperfect progressive
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has been sentinellingperfect progressive
Past
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sentineledsimple
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sentinelledsimple
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had sentineledperfect
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had sentinelledperfect
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was sentinelingprogressive
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was sentinellingprogressive
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were sentinelingprogressive
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were sentinellingprogressive
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had been sentinelingperfect progressive
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had been sentinellingperfect progressive
Future
Etymology
Origin of sentinel
First recorded in 1570–80; from Middle French sentinelle, from Italian sentinella, derivative of Old Italian sentina “vigilance,” from Latin sent(īre) “to feel” + -īna -ine 2
Explanation
A sentinel is a guard, a lookout, a person keeping watch. It's often a soldier, but not always. If you're watching a pot, waiting for it to boil, you're standing sentinel over it — and incidentally, it won't boil until you leave. Etymologists think sentinel stems from the Old Italian words sentina, meaning "vigilance," and sentire, "to hear or perceive." It's a close cousin of sentry, which means the same thing. You can use sentinel as a noun or a verb. A kid in a snowball war might be the sentinel, patrolling the entrance to the fort. Wolves stand sentinel over their kill, stepping aside only for the alpha male, who always eats first.
Vocabulary lists containing sentinel
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Common Senses: Sent, Sens ("Feel")
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
"When you only have a handful of species that can persist in environments like that, and they're really sensitive to change, those serve as really good sentinel taxa," Adams said.
From Science Daily ● Jan. 10, 2026
I wanted to ask him if he’d sign this book, which had now begun to write its own mythology as it sat sentinel over his other signed books on the shelf behind me.
From Los Angeles Times ● Jan. 8, 2026
Ahead of our return to the city, we drive back up the ridge, back through Burguete, the inn still shuttered, and up to Roncesvalles, where the old monastery looms like a sentinel over the pass.
From Salon ● Nov. 8, 2025
If musical theater had a canine sentinel, it might well be a standard French poodle.
From Los Angeles Times ● Nov. 18, 2024
The great sentinel was right there at the top of the ridge, where Will, had known it would be, its lowest branches a bare foot off the ground.
From "A Game of Thrones" by George R.R. Martin
The birds feed on insects living on rhinos and can also act as sentinels - calling to warn their hosts when danger approaches.
From BBC ● Aug. 25, 2026
“We stand on the walls, sentinels of the inner sanctum, against the assault of AI slop. The Ontology is based firmly in reality—there is, here, a dialectic between ground truth, tribal knowledge, and enhancements.”
From The Wall Street Journal ● May 5, 2026
“We stand on the walls, sentinels of the inner sanctum, against the assault of AI slop,” Karp said in his letter to shareholders.
From Barron's ● May 4, 2026
"Since dolphins are considered environmental sentinels for toxic exposures in marine environments," Dr. David Davis at the Miller School of Medicine explains, "there are concerns about human health issues associated with cyanobacterial blooms."
From Science Daily ● Oct. 11, 2025
Maybe it wasn’t bad, Sarai thought—she prayed—as she reached back out for her remaining sentinels.
From "Strange the Dreamer" by Laini Taylor
As by the elms that line its street, the hills that watch its roofs, Lyme, Conn., is sentineled by artistic good usage, fortressed by aesthetic tradition.
From Time Magazine Archive
A fort, mounting eight guns, sentineled the approach to the city from beneath, while the heights above were guarded by a three-banked battery.
From Sword and Pen Ventures and Adventures of Willard Glazier by John Algernon Owens
It began with the Old Senior Surgeon himself, who heard a pair of birds disputing in one of the two trees which sentineled the hospital.
From The Primrose Ring by Ruth Sawyer
With a couple of bounds he sentineled the doorway, barring the intended exodus.
From The Lash by Olin L. Lyman
At another point, emerging from a maze of mountains, the locomotive shoots into a plain, forty or fifty miles square, and sentineled on every side by savage peaks.
From John L. Stoddard's Lectures, Vol. 10 (of 10) Southern California; Grand Canon of the Colorado River; Yellowstone National Park by John L. (John Lawson) Stoddard
He was stationed at Fort Knox, where he sentinelled the country’s gold reserves.
From The New Yorker ● Mar. 27, 2017
Williamstown, sentinelled with maple trees, smiles at the Berkshires.
From Time Magazine Archive
Those who sentinelled the gate of the great kraal, Imvungayo, conferred a moment among themselves, and immediately two men were sent to learn the royal pleasure as to the request.
From The Sign of the Spider by Bertram Mitford
In the Close of Durdlebury, greenswarded, silent, sentinelled by immemorial elms that guard the dignified Gothic dwellings of the cathedral dignitaries, was James Marmaduke Trevor born.
From The Rough Road by William John Locke
She was slipping along very fast now, and Michael's keen glance swept the gray landscape to where, at the mouth of the channel, the treacherous Needles sentinelled the open sea.
From The Lamp of Fate by Margaret Pedler
The two great poplar-trees, sentineling what had once been the gate of the old Gordon homestead, had been spared through all the industrial changes.
From The Quickening by E. M. Ashe
The round green hills sentinelling the broad, expansive bosom of the Hudson held her attention by their beauty as the train followed the line of the stream.
From Sister Carrie: a Novel by Theodore Dreiser
The dry stalks, sentinelling the seared ground, waved their tattered remnants of unpicked bolls to and fro—summer's battle flags which had not yet fallen.
From The Bishop of Cottontown A Story of the Southern Cotton Mills by John Trotwood Moore
Dignity and grace lie in these tall swaying trees sentinelling the way on either side.
From In the Claws of the German Eagle by Albert Rhys Williams
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