Originally a pet form of Robert, from the short form Rob + the diminutive suffix -in (of Old French origin), but now nearly always used as an independent name. In recent years it has been increasingly used as a girl's name, partly under the influence of the vocabulary word denoting the bird.
Scottish and northern Irish: habitational name from what is now a deserted village in the parish of Barkby, Leicestershire. This is named from Old English hamel ‘crooked’ + dūn ‘hill’. Hamilton near Glasgow was founded by the Hamiltons and named after them. In Ireland, this name may have replaced Hamill in a few cases. It has also been used as the equivalent of the Irish (Cork) name Ó hUrmholtaigh.