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

Example Sentences

"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

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

The area has been named a sentinel landscape, a federally led effort to promote sustainable land-use practices near military installations.

From Los Angeles Times • May 23, 2024

He stepped up beside the silent sentinel on the dark edge, and Frodo followed.

From "The Two Towers" by J. R. R. Tolkien