n (context|optics) A lens which is convex on one side and concave on the other, being crescent-shaped in cross-section. (defdate|from 17th c.)
n The curved surface of liquids in tubes, whether concave or convex, caused by the surface tension of the liquid. (defdate|from 19th c.)
n (anatomy) Either of two parts of the human knee that provide structural integrity to the knee when it undergoes tension and torsion. (defdate|from 19th c.)