The name Decima is a girl's name of Latin origin meaning "tenth". Decima and is often added to lists like Cool Girl Names from Ancient Cultures and discussed in our forums with posts like "Change Two Letters".
From the experts:
In the days of huge families, this name of the Roman goddess of prophecy and childbirth, and one of the Fates, would be saved for bambina number ten. Now it might be used for a girl born in October, the tenth month.
Some other Latin numerical names you might consider: Octavia, Tertia, Una, Prima.