Medical Dictionary


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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