lu·nu·la 
(lnyə-lə)
(lnyə-lə)n. pl. lu·nu·lae (-lē′)
A small crescent-shaped structure or marking, especially the white area at the base of a fingernail that resembles a half-moon.
[New Latin lūnula, from Latin, crescent-shaped ornament, diminutive of lūna, moon; see leuk- in the Appendix of Indo-European roots.]