Its name is difficult to interpret: trechend means "three-headed", but ellén is an obscure word. One translator interprets it as a "swarm of three-headed creatures";"The Battle of Mag Mucrama", translator unknown, para 34 Whitley Stokes offered a "monstrous triple-headed bird" (Old Irish én, "bird");Whitley Stokes (ed. & tr.), "The Battle of Mag Mucrime", Revue Celtique 13, 1892, pp. 426-474 while T. F. O'Rahilly identifies it with Aillén, the fire-breathing monster fought by Fionn mac Cumhaill.T. F. O'Rahilly, Early Irish History and Mythology, Dublin Institute for Advanced Studies, 1946, p. 300
