sinus

 
Pronunciation: /ˈsʌɪnəs/

noun

  • 1 (often sinuses) Anatomy & Zoology a cavity within a bone or other tissue, especially one in the bones of the face or skull connecting with the nasal cavities.
  • an irregular venous or lymphatic cavity, reservoir, or dilated vessel.
  • Medicine an infected tract leading from a deep-seated infection and discharging pus to the surface.
  • Botany a rounded notch between two lobes on the margin of a leaf or petal.
  • 2 [as modifier] Physiology relating to or denoting the sino-atrial node of the heart or its function of regulating the heartbeat: sinus rhythm sinus tachycardia

Origin:

late Middle English (in the medical sense): from Latin, literally 'a recess, bend'