English, via Cecilia from the feminine of Caecilius, a Roman family name, from Latin "blind".

Caecilia was used in old documents for Cecily and Cecilia. Searching on Cecil* and Caecili* should find all these spelling variations, including Latin case endings.

Cecily does not occur in the 1841 Census of Aberdeenshire wheras the spellings Cicely and Cicily were used, albeit rarely.