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

Criteria air pollutants directly cause illnesses like sinus inflammation, lung and heart disease, cancers, and premature death because of how their physical properties interact with the human body. — Rebecca Florsheim, STAT, 17 July 2026

Symptoms of smoke inhalation include coughing, trouble breathing, wheezing, asthma attacks, stinging eyes, scratchy throat, runny nose and irritated sinuses, headaches, tiredness, chest pain and a fast heartbeat. — Michelle Del Rey, USA Today, 17 July 2026

Exposure can trigger respiratory problems and irritate sinuses and has been linked to more severe problems. — Victoria Craw, Washington Post, 16 July 2026

Suffering from a broken rib and sinus infection, Remco Evenepoel hands his bidon to a child on the roadside and dismounts his bike. — Jacob Whitehead, New York Times, 2 July 2026

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