A crescent moon, or an object shaped like it. [from 17th c.]
1959, Anthony Burgess, Beds in the East (The Malayan Trilogy), published 1972, page 554:
And from Crabbe's own forehead sweat dripped or gathered into a kind of meniscus to be scooped off.
1972, Vladimir Nabokov, Transparent Things, McGraw-Hill, published 1972, page 19:
He opened wide both casements; they gave on a parking place four floors below; the thin meniscus overhead was too wan to illumine the roofs of the houses descending toward the invisible lake [...].
(optics) A lens which is convex on one side and concave on the other, being crescent-shaped in cross-section. [from 17th c.]