meniscus

noun4

1. •
   A crescent moon, or an object shaped like it.

   • And from Crabbe's own forehead sweat dripped or gathered into a kind of meniscus to be scooped off. — 1959
2. •
   Either of two parts of the human knee that provide structural integrity to the knee when it undergoes tension and torsion.
3. •
   The curved surface of liquids in tubes, whether concave or convex, caused by the surface tension of the liquid.
4. •
   A lens which is convex on one side and concave on the other, being crescent-shaped in cross-section.