sentinel

American  

[sen-tn-l] / ˈsɛn tn l /

noun

1. 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.

   Synonyms:

   lookout, watch, guard, sentry

2. 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

   Synonyms:

   lookout, watch, guard, sentry

3. Digital Technology. tag.

4. 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.

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verb (used with object)

sentineled, sentineling, sentinelled, sentinelling

1. to watch over or guard as a sentinel.

   This monument sentinels each soldier's grave as a shrine.

adjective

1. Medicine/Medical. relating to or being an indication of a disease's presence or prevalence.

   Pregnant women attending prenatal appointments serve as a sentinel population for the prevalence of malaria in the region.

   The sentinel lymph nodes are the first lymph nodes that the cancer cells reach if they spread.

sentinel British  

/ ˈsɛntɪnəl /

noun

1. a person, such as a sentry, assigned to keep guard

2. computing a character used to indicate the beginning or end of a particular block of information

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verb

1. to guard as a sentinel

2. to post as a sentinel

3. to provide with a sentinel

Other Word Forms

• sentinellike adjective
• sentinelship noun
• unsentineled adjective
• unsentinelled adjective

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.

Example Sentences

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

The mean rescue sentinel did not think so.

From Salon • Dec. 6, 2024

The church stood empty like a silent sentinel over a small cemetery next to it.

From Slate • Oct. 24, 2024

Intriguingly, the system being attacked normally works as a sentinel or guard, whose job it is to detect invading viruses.

From Science Daily • May 23, 2024

The other side of the godswood, the sentinel, hurry, hurry ...

From "A Clash of Kings" by George R.R. Martin