meniscus

1:  a crescent or crescent-shaped body

2:  a fibrous cartilage within a joint:a:  either of two crescent-shaped lamellae of fibrocartilage that border and partly cover the articulating surfaces of the tibia and femur at the knee :  semilunar cartilage: (1):  one mostly between the lateral condyles of the tibia and femur—called also external semilunar fibrocartilage, lateral meniscus, lateral semilunar cartilage (2):  one mostly between the medial condyles of the tibia and femur—called also internal semilunar fibrocartilage, medial meniscus, medial semilunar cartilageb:  a thin oval ligament of the temporomandibular joint that is situated between the condyle of the mandible and the mandibular fossa and separates the joint into two cavities

3:  a concavo-convex lens

4:  the curved upper surface of a liquid column that is concave when the containing walls are wetted by the liquid and convex when not