sinus

noun

si·​nus ˈsī-nəs 

: 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

Here’s how to care for your eyes, sinuses and skin during a wildfire Jan. 10, 2025 On Sunday Zula Den, a nonprofit wellness center on Jefferson Boulevard, held a free wellness day that included acupuncture, massage, sound baths and reiki. —Deborah Vankin, Los Angeles Times, 15 Jan. 2025

The smoke can cause irritation to the eyes, skin, sinuses and nose, possibly resulting in stinging eyes and a runny nose. —Paul Du Quenoy, Newsweek, 9 Jan. 2025

Mucus is a substance that lines the moist surfaces of your body, like your lungs and sinuses, and helps your body fight illness. —Korin Miller, Health, 18 Dec. 2024

In adults, snoring can be caused by allergies, dietary choices (including alcohol consumption), and the anatomy of one's mouth and sinuses. —Daryl Austin, USA TODAY, 12 Dec. 2024

Word History

Etymology

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

First Known Use

15th century, in the meaning defined above

Phrases Containing sinus

• carotid sinus
• coronary sinus
• sinus node
• sinus rhythm
• sinus venosus
• urogenital sinus

Kids Definition

sinus

noun

si·​nus ˈsī-nəs 

: 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 

: 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