A recurring name in the Fenian Cycle, in both older manuscript materials and in later oral tradition; may describe one figure whose story has been dispersed and partially lost, or a sequence of figures whose stories have been confused. Ferdoman is usually seen as the son of an important Leinster family and as a young member of the Fianna. He is a protector of his younger sister, Finnine or Finngheal (also sometimes Finn), who is mistreated or killed by Conán mac Lia, sometimes described as her husband. Ferdoman avenges her in a duel in which both he and Conán are killed. According to different texts, Ferdoman also slays a monster, either a lake monster in Co. Offaly or a ferocious pig in Co. Donegal. Several elements, including his combat with the pig, suggest he is an anticipation of Diarmait ua Duibne.
See P. L. Henry, ‘An Irish-Icelandic parallel Ferdomun/ Karlsefni’, Ériu, 18 (1958), 158–9;Dáithí Ó hÓgáin, Fionn Mac Cumhaill (Dublin, 1988), 255–7.