Meniscus

Engineering definition
1.   A crescent or crescent-shaped body.
2.   A concave–convex lens.
3.   The curved upper surface of a column of liquid.

Medical definition
The piece of cartilage that lies mostly between the lateral condyles of the tibia and femur; also called the external semilunar fibrocartilage, lateral meniscus, or lateral semilunar cartilage.

Confusion
Because of different meanings in the engineering and medical fields, misunderstandings can easily occur where the two fields intersect, such as in the development of optics for medical procedures.