The etymology of Irland (Ériu, Erin, Hibernia, and Iverni)
“Gh” in Irish Like “ch” but based on a “g” sound gh= Eng. “y”, then the Celtic word rain (grain) could be pronounced yrain (Erin).
The etymology of Hibernia
havre: oat, wiktionary
From Old Norse hafri, from Proto-Germanic *habrô, from Proto-Indo-European *kapro-.
The cultivation of oats is particularly suited to Ireland’s climatic conditions and therefore oatmeal became a staple food of the Irish from prehistoric times until the seventeenth century.