Eochaid in Irish mythology (earlier, Eochu) is a name of mythical origin that occurs as that of several characters. It is a derivative of ech (later, each), which means ‘horse’, and the name is often associated with equine imagery.
The suggestion is that a deity could be envisaged as a great horseman, but in some contexts could indicate stallion-like reproductive ability (see Fergus mac Roich). The most striking instance of the namebeing attached to a divinity is that of the Dagda, who had the alternative designation of Eochaid Ollathair (i.e. Eochaid the Father of Many).
As appears from the rituals of Kingship, this father deity as the divine patron was represented by the sun. We may presume that the divine male principal was given a title such as ‘Eochaid Dagda’ (with a meaning such as ‘horseman the good god’), and was imagined as the presiding horseman of the heavens whose eye was the all-seeing sun…
Extract from: Ó hÓgáin, D. (2006). The Lore of Ireland: An Encyclopaedia of Myth, Legend and Romance. The Boydell Press. pp. 217-219
Eochaid in Irish mythology:
Lebor Gabala Erenn – The Book of Invasions. Part 4.
Tochmarc Etain – The Wooing of Etain
Some secondary sources:
Carmody, I. (2018) ‘Man of Peaks and Edges, Harp, Club and Cauldron, Eel and Otter Press,, pp. 12-38
Monaghan, P. 2008. The Encyclopedia of Celtic Mythology and Folklore. New York: Checkmark Books. pp. 155-156.
Koch, J.T. (ed.) 2006. Celtic Culture: A Historical Encyclopedia. Santa Barbara: ABC-CLIO. pp. 704-705..
MacKillop, J., 2004. A Dictionary of Celtic Mythology. Oxford: Oxford University Press. pp. 162-165.