The Collaborative International Dictionary of English v.0.48:
Fenian \Fe"ni*an\, n. [From the Finians or Fenii, the old
militia of Ireland, who were so called from Fin or Finn,
Fionn, or Fingal, a popular hero of Irish traditional
history.]
A member of a secret organization, consisting mainly of
Irishmen, having for its aim the overthrow of English rule in
Ireland.
[1913 Webster]
The Collaborative International Dictionary of English v.0.48:
Fenian \Fe"ni*an\, a.
Pertaining to Fenians or to Fenianism.
[1913 Webster]