There are two supposed Latinised forms of Cinuit/Cynuit/Cynwyd: Conuvitus and Cunetus – which at first sight appear to be quite separate. The form Conuvitus is found on a website discussing the dedication of Llangynwyd church. It gives no early source for it, nor for the alleged ‘English form’ Conowit (which is a modern surname found in the USA). So is Conuvitus just a conjectural reconstruction, derived from Cynuit? I shall assume so.
For sounder scholarship, the name of ‘St’ Cunetus is a good lead. Prof Orme (The Saints of Cornwall, p 93) states that in 1474, a Latin document relating to Llangynwyd refers to ‘beati Cuneti confessoris‘ and it seems the church was dedicated to ‘St’ Cunetus, with a feast day on 28 September.
How do we arrive at the form Cynwyd? In Old Welsh final unstressed vowels were lost in about the mid-6th.c., so Cunetus, or perhaps a purely Celtic form like *Coneto, would give Conet’ (probably still stressed on the same syllable, which had been the penultimate and now was the final). Diphthongisation of stressed vowels was beginning to occur at the same time, so Conet would become Coneit/Conuit. So Domesday forms such as Langenewit/Langunuit (modern Langunnet) would be possible derivations of Cunetus/*Coneto/Conet.
Prof Orme points to the name Conet which occurs as Conoit in Brittany in 871 and which appears in Breton and Cornish church names. Langonnet in Brittany, Langunnet (and Knett?) in Cornwall, Llangoned in a 16th c Will (later Llangynwyd) and Llantegonet (later Llandigwinnet) all support a connection with the name Conet, Latinised as Cunetus.
But who was St Cunetus/St Conet? WJ Rees in his Preface to Cambro British Saints describes the Lives as ‘legendary biographical accounts of several pious persons, who in the early age of the ancient British Church, obtained great eminence and distinction in Wales; and were called saints on account of their withdrawing themselves from secular concerns, and devoting their time and attention to religious matters, and particularly to the building of churches, and the founding of pious institutions.’ Miracles and canonisations were not necessary, but the pious persons often left no trace of their personal lives in written records.
And in any case, is this pious person in any way connected with arx Cynuit in Defenascire?