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

Summary Sleeping on an incline may be right for some people, and can help relieve certain symptoms or health conditions, such as obstructive sleep apnea, chronic sinus congestion, gastric reflux, fluid buildup in the lungs, and headaches. —Smita Patel, Verywell Health, 26 Apr. 2025

In much of the country, spring means pollen, mold and other allergens start playing havoc with our sinuses, skin and eyes. —Phaedra Trethan, USA Today, 26 Apr. 2025

This is when your sinuses become inflamed and swollen, blocking fluid drainage out of your sinuses and leading to fluid buildup in your inner ears. —Lindsay Curtis, Health, 25 Apr. 2025

This can loosen mucus in your lungs and sinuses, ease a sore throat, and help with congestion. —Anna Giorgi, Verywell Health, 7 Apr. 2025

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

Rhymes for sinus

• coyness
• dryness
• highness
• linus
• minus
• pinus
• shyness
• busyness
• equinus

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