A Cymric and Irish Goddess, also known as Niamh: Brightness, Radiance
Nyf (Brightness, Radiance) is a Cymric (Welsh) and Irish goddess known from the Irish Fenian and Ulster cycles and is given in the list of heroes of Arthur’s court in the Mabinogi of Culhwch ac Olwen and she is the woman who cares for CúChulain during his illness.
Nyf is one of a number of heroes of the Irish Fenian and Ulster cycles (another being Derdri mentioned by Gogynfeirdd such as Dafydd ap Gwilym and Lewis Glyn Cothi; whilst the names of other Ulster heroes such as Ffin vab Koel (Fionn mac Cumhaill) have been incorporated into the lists of heroes given in the Mabinogion of Culhwch ac Olwen. This strongly indicates that the Fenian and Ulster cycles were known to the early Cymric storytellers and that some of these legends lasted long into the medieval period. Knowledge of these tales probably came from the Old North, from the links between the peoples of Ystradclud (Strathclyde) and Ulster. This may explain why echoes of the northern character, Drystan is seen in the Ulster cycle and why CùChulain goes to the isle of Arran to learn the feats of weapons. Indeed, there would seem to have been a movement of people from southern Scotland to Northern Ireland and vice-versa for at least 5000 years.
Though the orthography of the Cymric form Nyf and the Gaelic Niamh are very different the pronunciations are almost identical (and can be approximated in English as Neev) so that we can be confident they represent the same person. However, there are several Niamhs in Irish mythos though the Cymric Nyf probably refers to the Niamh of the Tain nurse and sometime lover of CúChulain. Niamh was the daughter of Celthair of the Red Branch and sometime wife of Conall Cearnach (whose other consort was Lendabair). It is Niamh who, at Conchobar’s insistence (and being in love with him herself) cares for CúChulain after he is laid low with confusion due to the enchantments of the one-eyed daughters of Cailitin (CúChulain having slain their father and all of their brothers). Under Conchobar’s insistence and from Niamh’s persuasion CúChulain is taken to Gleann-na-Bodhar (The Valley of Deafness) and in that place’s perfect tranquillity Niamh persuades him to give his word that he would not go out and meet the men of Ireland without leave from her. CúChulain gives his word and agrees to stay with her. However, Badb, the daughter of Cailitin puts a spell on Niamh by impersonating one of her handmaidens and entices her from the hero’s bedside. Badb then assumes Niamh’s form and entering CúChulain’s chamber bids the hero rise from his bed; and thus begins the journey that eventually results in the hero’s death.