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
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
How antibiotics can affect your gut bacteria Antibiotics are medications prescribed to treat many different types of bacterial infections, like sinus infections, strep throat, urinary tract infections (UTIs), pelvic infections, and bacterial vaginosis (BV).
—Beth Krietsch, SELF, 7 Apr. 2025
Applying slight pressure to these areas can relieve jaw tension, headaches, and sinus pain.
—Kiana Murden, Vogue, 13 Mar. 2025
See All Example Sentences for sinus
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Andrea Muraskin, NPR, 19 Apr. 2025
How is a fungal sinus infection diagnosed and treated?
—Laura Schober, Health, 14 Apr. 2025
How antibiotics can affect your gut bacteria Antibiotics are medications prescribed to treat many different types of bacterial infections, like sinus infections, strep throat, urinary tract infections (UTIs), pelvic infections, and bacterial vaginosis (BV).
—Beth Krietsch, SELF, 7 Apr. 2025
Applying slight pressure to these areas can relieve jaw tension, headaches, and sinus pain.
—Kiana Murden, Vogue, 13 Mar. 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 3 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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