lunula

lunulae

You know how we refer to anything to do with the moon as "lunar"? Well, that word plays into the meaning of lunula, which is something with a curved, half-moon shape — like the white at the base of your fingernails.

The Latin word for moon is lūna, which was also one of the name of the Roman moon goddess. From that we get lunula, which is the name of the nail matrix, the living part of the fingernail and toenail, a visible white, half-moon-shape at the nail’s base. Here's a spelling hint: the plural of lunula is lunulae, adding an e instead of an s, a spelling rule peculiar to words that have a Latin origin and end in a.