Transferred use of the Irish surname, Gaelic form Ó Sluaghhadáin (‘descendant of Sluaghadhán’). The latter is a diminutive of the personal name Sluaghadh, meaning ‘expedition, raid’. Recently the surname has occasionally been used as a given name, mainly in the United States.
Scottish: habitational name from a place in Huntingdonshire (now part of Cambridgeshire), so called from Old English hramsa ‘wild garlic’ + ēg ‘island’, ‘low-lying land’. There are other places in England called Ramsey, but the one in Huntingdonshire is almost certainly the source of the surname. The usual spelling of the surname in Scotland is Ramsay.