sinus

noun

si·​nus ˈsī-nəs How to pronounce sinus (audio)
: cavity, hollow: such as
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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The explanation might be a deviated septum, but a growth inside the nose or sinuses can also block one side. — Angela Haupt, Time, 16 Oct. 2026 Pseudoephedrine pills or nasal spray can relieve a stuffy nose or sinus pressure by restricting blood vessels and opening airways in your nasal passages. — Andee Tagle, NPR, 15 Oct. 2026 Among several sauces on the side, home in on senafich, a classic, sinus-sizzling Ethiopian condiment fashioned from mustard seeds. — Bill Addison, Los Angeles Times, 11 Oct. 2026 Dr Xu had submitted a short video showing tiny, hair-like structures called cilia moving through the airway of a child suffering from primary ciliary dyskinesia, a rare respiratory condition that can lead to chronic lung, sinus, and ear infections. — Will McCurdy, PC Magazine, 11 Oct. 2026 See All Example Sentences for sinus

Word History

Etymology

Middle English, from Medieval Latin, from Latin, curve, fold, hollow

First Known Use

15th century, in the meaning defined above

Time Traveler
The first known use of sinus was in the 15th century

Phrases Containing sinus

Rhymes for sinus

See All Rhymes for sinus

Browse Nearby Words

sinuous
sinus
sinus gland
See all Nearby Words

Cite this Entry

“Sinus.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/sinus. Accessed 20 Oct. 2026.

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Kids Definition

sinus

noun
si·​nus ˈsī-nəs How to pronounce sinus (audio)
: a hollow place : cavity
especially : any of several cavities in the skull that usually connect with the nostrils

Medical Definition

sinus

noun
si·​nus ˈsī-nəs How to pronounce sinus (audio)
: 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

More from Merriam-Webster on sinus

Britannica.com: Encyclopedia article about sinus

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