Latinate form of French Henriette. Henrietta Maria (1609–69), the wife of King Charles I, was the daughter of Henry IV of France, in whose honour the name was sometimes chosen by gentry families in the 17th century. It enjoyed a revival in the late 19th century. See also Harriet.
Irish: Anglicized form of Gaelic Ó Ceallaigh ‘descendant of Ceallach’, an ancient Irish personal name, originally a byname meaning ‘bright-headed’, later understood as ‘frequenting churches’ (Irish ceall). There are several early Irish saints who bore this name. Kelly is now the most common of all Irish family names in Ireland.