a
: a narrow elongated tract extending from a focus of suppuration and serving for the discharge of pus
b(1)
: a cavity in the substance of a bone of the skull that usually communicates with the nostrils and contains air
(2)
: a channel for venous blood
(3)
: a dilatation in a bodily canal or vessel
c
: a cleft or indentation between adjoining lobes (as of a leaf or corolla)
Examples of sinus in a Sentence
Recent Examples on the Web
Inhaling the steam from and consuming a hot beverage (like water) can help with nasal congestion by breaking up mucus and unclogging the sinuses.
—
Cristina Mutchler, Verywell Health, 9 Feb. 2026
Signs that a neti pot may be dirty or causing issues for another reason include persistent nasal irritation, worsening congestion, frequent nosebleeds or the development of sinus infections.
—Daryl Austin, USA Today, 8 Feb. 2026
Her doctor thought something might be wrong with her sinuses.
—CBS News, 7 Feb. 2026
Will influencers start selling high-end neti pots to clean out our sinuses in the hopes of shrinking our noses?
—Georgia Casey, Allure, 6 Feb. 2026
See All Example Sentences for sinus
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Cristina Mutchler, Verywell Health, 9 Feb. 2026
Signs that a neti pot may be dirty or causing issues for another reason include persistent nasal irritation, worsening congestion, frequent nosebleeds or the development of sinus infections.
—Daryl Austin, USA Today, 8 Feb. 2026
Her doctor thought something might be wrong with her sinuses.
—CBS News, 7 Feb. 2026
Will influencers start selling high-end neti pots to clean out our sinuses in the hopes of shrinking our noses?
—Georgia Casey, Allure, 6 Feb. 2026
See All Example Sentences for sinus
Cite this Entry
“Sinus.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/sinus. Accessed 16 Feb. 2026.
Copy CitationKids Definition
Medical Definition
sinus
noun
si·nus
ˈsī-nəs 
: a cavity or hollow in the body: as
a
: a narrow elongated tract extending from a focus of suppuration and serving for the discharge of pus
a tuberculous sinus
b(1)
: a cavity in the substance of a bone of the skull that usually communicates with the nostrils and contains air
(2)
: a channel for venous blood
(3)
: a dilatation in a bodily canal or vessel
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