Fenian
noun
Fe·ni·an ˈfē-nē-ən 
1
: a member of a legendary band of warriors defending Ireland in the second and third centuries a.d.
2
: a member of a secret 19th century Irish and Irish-American organization dedicated to the overthrow of British rule in Ireland
Fenian adjective
Fenianism
ˈfē-nē-ə-ˌni-zəm
noun 
Word History
Etymology
Fen- (probably in part from Middle Irish Féni freeholders, legendary settlers of Ireland, in part from Irish fiann, genitive singular féinne band of warriors) + -ian
First Known Use
1816, in the meaning defined at sense 1