sinus

noun7

1. •
   A pouch or cavity in a bone or other tissue, especially one in the bones of the face or skull connecting with the nasal cavities (the paranasal sinus).
2. •
   An irregular venous or lymphatic cavity, reservoir, or dilated vessel.
3. •
   An abnormal cavity or passage such as a fistula, leading from a deep-seated infection and discharging pus to the surface.
4. •
   [before a noun] Relating to or denoting the sinoatrial node of the heart or its function of regulating the heartbeat.
5. •
   A rounded notch or depression between two lobes or teeth in the margin of a leaf or petal.
6. •
   A bay of the sea; a recess in the shore.
7. •
   Synonym of sine.

   • The variations are described in terms of cycles of sinuses and cosinuses. — 1996