Domitilla is the Latin feminine diminutive of Domitius — meaning "little tame one" or "little one of the household." Saint Flavia Domitilla (1st c.) was a Roman noblewoman martyred for her Christian faith — niece of Emperors Titus and Domitian.
The Catacombs of Domitilla in Rome — Christian burial caves — were named after her.
Domitilla reduces to seven — the number of Roman household.