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
That same elevation helps drain sinus congestion from seasonal allergies.
—
Allison Palmer, Miami Herald, 9 Apr. 2026
That same slight elevation helps drain mucus and relieve sinus congestion from seasonal allergies.
—Allison Palmer, Sacbee.com, 9 Apr. 2026
That same elevation also helps drain mucus and ease congestion from seasonal allergies, which is a useful bonus if sinus issues compound your sleep troubles.
—Allison Palmer, Fort Worth Star-Telegram, 9 Apr. 2026
Rethinking How Nasal Congestion Is Treated Nasal congestion develops because nasal passage tissues swell due to inflammation, which obstructs breathing and prevents mucus from exiting the sinus cavities.
—Matthew Kayser, USA Today, 25 Mar. 2026
See All Example Sentences for sinus
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Allison Palmer, Miami Herald, 9 Apr. 2026
That same slight elevation helps drain mucus and relieve sinus congestion from seasonal allergies.
—Allison Palmer, Sacbee.com, 9 Apr. 2026
That same elevation also helps drain mucus and ease congestion from seasonal allergies, which is a useful bonus if sinus issues compound your sleep troubles.
—Allison Palmer, Fort Worth Star-Telegram, 9 Apr. 2026
Rethinking How Nasal Congestion Is Treated Nasal congestion develops because nasal passage tissues swell due to inflammation, which obstructs breathing and prevents mucus from exiting the sinus cavities.
—Matthew Kayser, USA Today, 25 Mar. 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 20 Apr. 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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