sinus

noun

Etymology: Learned borrowing from Latin sinus (“a bent surface, curve, hollow”). Doublet of sine.

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 irregular venous or lymphatic cavity, reservoir, or dilated vessel.
4. An abnormal cavity or passage such as a fistula, leading from a deep-seated infection and discharging pus to the surface.
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.

   “So, in the helicopteron, as the helix is at the same time a sustaining plane, it should be likened to a surface moving horizontally, and in which, consequenty, the resistance to motion will be to the lifting power as the sinus is to the cosinus of the angle formed by such plane with the horizon.”

   “The variations are described in terms of cycles of sinuses and cosinuses.”