Dictionary

sinus

noun si·nus \ˈsī-nəs\

: any of several spaces in the skull that connect with the nostrils

Full Definition of SINUS

:  cavity, hollow: 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)
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Origin of SINUS

Middle English, from Medieval Latin, from Latin, curve, fold, hollow
First Known Use: 15th century
SINUS Defined for Kids

sinus

noun si·nus \ˈsī-nəs\

Definition of SINUS for Kids

:  any of several spaces in the skull mostly connected with the nostrils
Medical Dictionary

sinus

noun si·nus \ˈsī-nəs\

Medical Definition of SINUS

:  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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