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
By the end of the mission, 10 days after Schirra first started feeling sick, the crew’s sinuses were still plugged with mucus.
—
Kiona N. Smith, Forbes, 12 Mar. 2025
Chronic rhinosinusitis is long-term inflammation of your sinuses as well as the nasal passages.
—Lindsay Curtis, Health, 5 Mar. 2025
The program reported that chronic rhinosinusitis, a condition affecting the sinuses, stands as the most common illness associated with the attack, with nearly 27,250 responders and almost 6,200 survivors reporting it.
—Matt Robison, Newsweek, 18 Feb. 2025
Try eating hot soup or broth to help thin mucus, drain the sinuses, and soothe throat irritation.38
13.
—Ann Pietrangelo, Verywell Health, 10 Feb. 2025
See All Example Sentences for sinus
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Kiona N. Smith, Forbes, 12 Mar. 2025
Chronic rhinosinusitis is long-term inflammation of your sinuses as well as the nasal passages.
—Lindsay Curtis, Health, 5 Mar. 2025
The program reported that chronic rhinosinusitis, a condition affecting the sinuses, stands as the most common illness associated with the attack, with nearly 27,250 responders and almost 6,200 survivors reporting it.
—Matt Robison, Newsweek, 18 Feb. 2025
Try eating hot soup or broth to help thin mucus, drain the sinuses, and soothe throat irritation.38
13.
—Ann Pietrangelo, Verywell Health, 10 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 23 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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