The surname Gearin and variations thereof likely arose independently multiple times in Western Europe. In Ireland, it is probably derived from Ó Gearáin, perhaps a diminutive of the Old Irish, “gér,” meaning “sharp,” “intelligent,” and “piercing.” In England and continental Europe, Gearin may variously derive from “guerre” meaning “war” or “gār” and “geirr” which mean “spear,” and which share their etymology with Old Irish, “gér” through from Proto-Celtic *gaisos, and Proto-Germanic *gaizaz. Both roots have cognates in Old English, Old French, and Old Norse, which may have resulted in contemporaneous families with non-shared ancestries to adopt the surname. Prior to the standardization of English spelling, it is likely that unrelated families in the same region went by phonetically similar but etymologically distinct surnames resulting in homophone and heteronym “Gearin’s”. For example, the Norman Invasion of England and Ireland, the settling of the Huguenots in Ireland, and the Gaelicization of foreign words could have led to Gearin’s and Guerin’s living in close proximity, with their spellings being only imperfect clues to their respective etymologies. Similarly, not all perceived variations of the Gearin surname are apt to share a root with Old Irish “gér.” For example, the surnames Geary, Guaire, and Gerring are often identified as variants of Gearin. Though these names are phonetically similar to Gearin in Modern English and could have potentially resulted in Gearin surnames, they sounds considerably less similar to Gearin in Old, Middle, and Modern Irish, and have distinct presumed etymologies.