Hej CN,
I found this in the book 'A-Z of Irish Names for Children and their meanings' by
Diarmaid Ó Muirithe:
"FERDIA earlier FER DÉA, FER DEODA, FER DEADH, FER DIADH (m)
There are many variants of the name in medieval literature all of which associate him with divinity or fire. A fictional warrior in the Ulster Cycle, in the Táin Bó Cuailnge his epic fight with his friend Cú Chulainn at the ford is described with great drama. In some recensions of the tale they beseech each other to stop fighting and recall their past friendship. They embrace and give one another healing herbs, food and drink. But on the third evening they break all contact with one another and resume mortal combat, using all the tricks they know. Cú Chulainn's charioteer sends his spear, the ga bolga, downstream to him, and flinging it from between his toes wounds Fer Diadh in the anus.
He lowers his shield, and Cú Chulainn pierces him through the heart.
He dies in the arms of his old friend. Ferdia is still given to children in the area connected with the Táin, the town of Ardee in Co. Louth, in Irish Áth Fhir Diadh (the ford of Fer Diadh)."
According to encyclopedia.com, Gaelic fer diad means "man of smoke"
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Satu
http://www.nordicnames.de/