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
Angela Craig had been taking it due to a sinus infection, the prosecution said.
—
Alisha Ebrahimji, CNN Money, 31 July 2025
Last month, a 71-year-old Texas woman died from the brain-eating amoeba after flushing her sinuses with tap water, health officials said.
—Muri Assunção, New York Daily News, 23 July 2025
The tingle of lemongrass, kaffir lime and galangal ride the sour pop that springs right up into your sinuses and evokes fragrant memories of Thailand.
—Matthew Odam, Austin American Statesman, 2 July 2025
And that’s nothing compared to the sinus pressure, brain fog, and relentless congestion that turns everyday tasks into uphill climbs.
—Tanya Benedicto Klich, Forbes.com, 27 June 2025
See All Example Sentences for sinus
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Alisha Ebrahimji, CNN Money, 31 July 2025
Last month, a 71-year-old Texas woman died from the brain-eating amoeba after flushing her sinuses with tap water, health officials said.
—Muri Assunção, New York Daily News, 23 July 2025
The tingle of lemongrass, kaffir lime and galangal ride the sour pop that springs right up into your sinuses and evokes fragrant memories of Thailand.
—Matthew Odam, Austin American Statesman, 2 July 2025
And that’s nothing compared to the sinus pressure, brain fog, and relentless congestion that turns everyday tasks into uphill climbs.
—Tanya Benedicto Klich, Forbes.com, 27 June 2025
See All Example Sentences for sinus
Cite this Entry
“Sinus.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/sinus. Accessed 20 Aug. 2025.
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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