meniscus

noun

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.”

   “He opened wide both casements; they gave on a parking place four floors below; the thin meniscus overhead was too wan to illumine the roofs of the houses descending toward the invisible lake [...].”

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.