1. [noun] A crescent moon, or an object shaped like it. [from 17th c.]
2. [noun] (optics) A lens which is convex on one side and concave on the other, being crescent-shaped in cross-section. [from 17th c.]
3. [noun] The curved surface of liquids in tubes, whether concave or convex, caused by the surface tension of the liquid. [from 19th c.]
4. [noun] (anatomy) Either of two parts of the human knee that provide structural integrity to the knee when it undergoes tension and torsion. [from 19th c.]
5. [noun] (anatomy) a disk of cartilage that serves as a cushion between the ends of bones that meet at a joint.
6. [noun] (optics) a lens that is concave on one side and convex on the other.
7. [noun] (physics) the curved upper surface of a nonturbulent liquid in a vertical tube.
