Origin: < pl. of Ir Gael Fiann, the old militia of Ireland, after Finn, Fionn, hero of Irish tradition: assoc. with OIr fēne, inhabitant of Ireland
See Fenian in American Heritage Dictionary 4
Origin: From alteration (influenced by féne, body of freemen under early Irish law)
Origin: of Irish Gaelic fianna, bands of young warriors
Origin: , from Old Irish fíanna
Origin: , pl. of fían.