Me-nis'ēus, n.

noun

n.; pl. ME-NĪS'ĒUS-ES. [Gr. μη-νίσκος, diminutive of μήνη, the moon, hence, any moon-shaped body.] (Opt.) A lens convex on one side and concave on the other, having the concavity less than the convexity.

A narrow crescent-shaped curved figure.
Menis- cus.