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
This is when your sinuses become inflamed and swollen, blocking fluid drainage out of your sinuses and leading to fluid buildup in your inner ears.
—
Lindsay Curtis, Health, 25 Apr. 2025
This can loosen mucus in your lungs and sinuses, ease a sore throat, and help with congestion.
—Anna Giorgi, Verywell Health, 7 Apr. 2025
Pointing the spray bottle towards the ear also targets openings between your nasal passages and your sinuses, lowering your risk of developing a sinus infection, says Rubin.
6.
—Andrea Muraskin, NPR, 19 Apr. 2025
How is a fungal sinus infection diagnosed and treated?
—Laura Schober, Health, 14 Apr. 2025
See All Example Sentences for sinus
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Lindsay Curtis, Health, 25 Apr. 2025
This can loosen mucus in your lungs and sinuses, ease a sore throat, and help with congestion.
—Anna Giorgi, Verywell Health, 7 Apr. 2025
Pointing the spray bottle towards the ear also targets openings between your nasal passages and your sinuses, lowering your risk of developing a sinus infection, says Rubin.
6.
—Andrea Muraskin, NPR, 19 Apr. 2025
How is a fungal sinus infection diagnosed and treated?
—Laura Schober, Health, 14 Apr. 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 May. 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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