From Old Irish, cognate with either Féni (“Irish People”), from Proto-Indo-European *weydh- (“wood, wilderness”)); or fían (“war band”) (from Proto-Indo-European *weyh₁- (“chase, pursue, suppress”)).
From the name of the area of Wales, or perhaps from gwyn (“white, fair”).
|Note: Some of these forms may be hypothetical. Not every
possible mutated form of every word actually occurs.