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
As his doctor, Kevin O'Connor, noted in a 2019 report released by Biden's presidential campaign team, his symptoms initially improved with nasal and sinus surgeries.
—
Maria Sokolina, Forbes, 25 Feb. 2025
Sinusitis: Also known as a sinus infection, sinusitis causes headaches and sinus pressure.
—Mark Gurarie, Verywell Health, 24 Feb. 2025
Upper respiratory tract infections affect the sinuses and throat and would include infections like the common cold and a sinus infection.
—Katia Hetter, CNN, 19 Feb. 2025
On the moderate end, flu patients may go on to develop ear or sinus infections.
—Thomas G. Moukawsher, Newsweek, 11 Feb. 2025
See All Example Sentences for sinus
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Maria Sokolina, Forbes, 25 Feb. 2025
Sinusitis: Also known as a sinus infection, sinusitis causes headaches and sinus pressure.
—Mark Gurarie, Verywell Health, 24 Feb. 2025
Upper respiratory tract infections affect the sinuses and throat and would include infections like the common cold and a sinus infection.
—Katia Hetter, CNN, 19 Feb. 2025
On the moderate end, flu patients may go on to develop ear or sinus infections.
—Thomas G. Moukawsher, Newsweek, 11 Feb. 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 9 Mar. 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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