sinus
noun
[ ˈsʌɪnəs ]
• a cavity within a bone or other tissue, especially one in the bones of the face or skull connecting with the nasal cavities.
• relating to or denoting the sino-atrial node of the heart or its function of regulating the heartbeat.
• "sinus rhythm"
Origin:
late Middle English (in the medical sense): from Latin, literally ‘a recess, bend’.
