Definition of cassidy:
(n) :
A male given name transferred from the surname.
(n) :
A female given name transferred from the surname, of modern American usage.
(n) :
A surname from Irish anglicized from Ó Caiside (“descendant of Caiside”). Caiside is a byname from Irish cas (“curly”) meaning “curly-haired”.
(n) :
A surname from Irish, a rare anglicization of Mac Casarlaigh (Casserly).
(n) :
A community in southern Vancouver Island, British Columbia, Canada.