meniscus

noun

1. A crescent moon, or an object shaped like it.
2. A lens which is convex on one side and concave on the other, being crescent-shaped in cross-section.
3. The curved surface of liquids in tubes, whether concave or convex, caused by the surface tension of the liquid.
4. Either of two parts of the human knee that provide structural integrity to the knee when it undergoes tension and torsion.