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
But pollen also messes with sleep, ups the risk of sinus infections, causes people to miss school and work, and can pose more serious dangers.
—
Keerti Gopal, ArsTechnica, 8 May 2026
In studies, bromelain has been shown to reduce pain and swelling associated with sinus infections and dental problems, as well as to speed up wound healing, especially burns.2223
8.
—Sarah Bradley, Health, 27 Apr. 2026
People who sleep on their backs often feel worse at night because lying flat makes congestion worse by letting mucus pool in the sinuses.
—Helen Carefoot, Flow Space, 14 Apr. 2026
The eye sinuses almost certainly arose first for thermoregulation in a harsh desert climate.
—Ryan Brennan, Kansas City Star, 13 Apr. 2026
See All Example Sentences for sinus
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Keerti Gopal, ArsTechnica, 8 May 2026
In studies, bromelain has been shown to reduce pain and swelling associated with sinus infections and dental problems, as well as to speed up wound healing, especially burns.2223
8.
—Sarah Bradley, Health, 27 Apr. 2026
People who sleep on their backs often feel worse at night because lying flat makes congestion worse by letting mucus pool in the sinuses.
—Helen Carefoot, Flow Space, 14 Apr. 2026
The eye sinuses almost certainly arose first for thermoregulation in a harsh desert climate.
—Ryan Brennan, Kansas City Star, 13 Apr. 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 13 May. 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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