This place-name is poorly attested and its origin is unclear. No Modern or Middle English precursor readily suggests itself, and although it is possible that the name may be derived from Irish coll “hazel(-tree)”, as O’Donovan suggests (5) (see also BPP p.49), the occurrence of that word as a place-name in simplex form would be exceptional (cf. Corpas, Onomasticon). It is not implausible, therefore, that the name of Cull Island, which sits above the surrounding tidal marsh, might be derived from the Norse word kollr “a hill”. However, the number of Norse place-names in Ireland is so small, and the evidence here so slight, that this interpretation is very uncertain (see Introduction). As the etymology of this place-name remains unclear it is deemed appropriate to recommend the phonetic approximation Coll as the Irish form of the name here.

[Excerpt from Logainmneacha na hÉireann IV: Townland Names of County Wexford, 2016]