Cassidy
An Irish surname from Ó Caiside, traditionally linked to a “clever” or “curly-haired” ancestor, though some old sources read it as “one who complains or accuses.”
The #1,325 most common surname in the United States (2010 Census) — about 1 in every 11,611 Americans shares it.
Etymology
Cassidy is the Anglicized form of Irish Ó Caiside, meaning “descendant of Caiside.” The personal name Caiside is usually connected with Irish cas, meaning “curly” or “twisted,” which may point to curly hair or a descriptive nickname; one older interpretation also connects it with the idea of cleverness or ingenuity. An older 19th-century source instead explained it from casaideach, meaning “apt to complain or accuse,” but that analysis is less widely accepted.
History
The name is strongly associated with Irish families, especially in Ulster, and appears frequently in historical Irish records and surname studies. In the 20th century it remained a distinctly Irish surname and spread widely through emigration, especially to Britain, the United States, and other English-speaking countries.
Origin
Regions
Variant spellings
Fun fact
The hereditary medical family Ó Caiside was well known in medieval Ireland, and the surname survives today in several Anglicized spellings.
From the historical record
“the radical sense of hatred is driving off. CASSIDY. (Gaelic.) From casaideach, apt to complain or accuse. Casadow, in the Cor. Br., signifies an offender. CATHCART. (Gaelic.) Local. From the parish of Cathcarf^ in Lanark and Renfrew, Scotland. The river Cart runs through it, whence the name is derived. Caeth-…”
— An Etymological Dictionary of Family and Christian Names