Meniscus \Me*nis"cus\, n.; pl. L. {Menisci} (-s[=i]), E. {Meniscuses}. [NL., from Gr. ?, dim. of mh`nh the moon.] 1. A crescent. 2. (Opt.) A lens convex on one side and concave on the other. 3. (Anat.) An interarticular synovial cartilage or membrane; esp., one of the intervertebral synovial disks in some parts of the vertebral column of birds. {Converging meniscus}, {Diverging meniscus}. See {Lens}.