Latinate feminine form of the Roman family name Caecilius, which was derived from Latin caecus "blind". Saint Cecilia was a semi-legendary 2nd- or 3rd-century martyr who was sentenced to die because she refused to worship the Roman gods. After attempts to suffocate her failed, she was beheaded. She was later regarded as the patron saint of music and musicians.
Due to the popularity of the saint, the name became common in the Christian world during the Middle Ages. The Normans brought it to England, where it was commonly spelled Cecily - the Latinate form Cecilia came into use in the 18th century.