McGreevy is the English phonetic pronunciation of Mag Riabhaigh. Without going to Farr into the rules of Gaelic grammar Riabhaigh is the genitive case of the word Riabhach which means Grey or Brindled. In this case it probably applies to facial and head hair, (I'm not sure about all other mcgreevy clans but my own family have a history of early greying and different colored facial hair from head hair, usually black head hair and red beard). History records that McGreevy originated in Roscommon but also that Down is an early settlement of McGreevy. McGreevy was indeed ancient king of the territory around Roscomon, Sligo Mayo. Recent high profile McGreevy's include Jim McGreevy former governor of New Jersey and prospective President of the USA. His ancestors hail from county Down. Other forms of the name:McCreevy, Creevy, Reagh, Grey. Hope this was of some help.