O’. [Ir. o a descendant.] A prefix to Irish family names, which signifies grandson or descendant of, and is a character of dignity; as O’Neil, O’Carrol.

O’ (o; unaccented o), prep. A shortened form of of or on. "At the turning o’ the tide." Shak.

O’er, prep. & adv. A contr. of Over. [Poetic]