annwfn

“The 'annwfn' of the Welsh was distinctly conceived in the folk-lore embodied in mediaeval poetry as being 'is elfydd' (beneath the world).”

Celtic Religion in Pre-Christian Times

“_Annwn_, which has been increased by the very frequent mistake of writing it _Anwn_, which means, _unknown_, _strange_, and is applied to the people who dwell in the antipodes of the speaker; while _Annwn_ is an adaptation of _annwfn_, a _bottomless_ or _immeasurable pit_,”

Notes and Queries, Number 19, March 9, 1850