What is the original meaning of the word meniscus?

Meniscus stands for: Small month (small moon). ΜΗΝ in Greek language, stands for "month", and meniscus refers to the shape of the waxing (or waning) crescent moon.

The suffix -iscus, stands for "little" just like -let /-ling /-ster. so, meniscus = "monthling", "monthster".