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
Recurrent lesions in the same location or the development of tunnels (sinus tracts) can indicate more advanced disease and may require surgical or higher-level intervention.
—
Lauryn Higgins, Flow Space, 18 May 2026
Cancers of the head and neck include malignancies affecting the mouth and throat (called the oral cavity and pharynx), the voice box (larynx), the sinuses and nasal cavities, and the salivary glands.
—Mikkael Sekeres, Washington Post, 18 May 2026
Slices of cold roast beef, beautiful and rare, come attended by a snowy blob of properly sinus-clearing horseradish cream, with a pickled black walnut on top like the cherry on a sundae and a crumbly wedge of cheddar.
—Helen Rosner, New Yorker, 17 May 2026
Stepping into a warm shower opens our pores and our sinuses, and if there's mildew or mold on a soggy bath linen, gives those allergens an easy pass straight into our bodies.
—Mary Catherine McAnnally Scott, Southern Living, 12 May 2026
See All Example Sentences for sinus
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Lauryn Higgins, Flow Space, 18 May 2026
Cancers of the head and neck include malignancies affecting the mouth and throat (called the oral cavity and pharynx), the voice box (larynx), the sinuses and nasal cavities, and the salivary glands.
—Mikkael Sekeres, Washington Post, 18 May 2026
Slices of cold roast beef, beautiful and rare, come attended by a snowy blob of properly sinus-clearing horseradish cream, with a pickled black walnut on top like the cherry on a sundae and a crumbly wedge of cheddar.
—Helen Rosner, New Yorker, 17 May 2026
Stepping into a warm shower opens our pores and our sinuses, and if there's mildew or mold on a soggy bath linen, gives those allergens an easy pass straight into our bodies.
—Mary Catherine McAnnally Scott, Southern Living, 12 May 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 21 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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