Fenian

noun

1. any of a group of legendary military heroes of ancient Ireland
2. ☆ a member of a secret revolutionary movement formed in New York and Ireland to free Ireland from English rule: the movement was most active in the 1860s and continued until WWI

Etymology: < pl. of Ir Gael Fiann, the old militia of Ireland, after Finn, Fionn, hero of Irish tradition: assoc. with OIr fēne, inhabitant of Ireland

adjective

of the Fenians