Hilaria is the feminine of Hilarius — from Latin hilaris (cheerful, joyful). Saint Hilaria (4th c.) was the daughter of Emperor Zeno, who fled an arranged marriage and lived disguised as a monk in the desert of Scetis for years.
The Roman festival of Hilaria celebrated the resurrection of Attis each March — a precursor to Easter joy.
Hilaria reduces to nine — the number of Roman cheer.