Getting ahead of myself again, but I happened to be looking online for information about the Welsh poet Gillian Clarke, and I came across a quote from one of her poems in Welsh. (I’m sorry to say I hadn’t even realised she wrote in Welsh too: if her Welsh poems are as good as her English ones that’s really impressive). Anyway, the quote was from a poem called ‘Llong Casnewydd’ and it runs ‘Hwyliau bratiog o wylanod sy’n araf lithro uwch gewynau gwinau-lydan afon Wysg’. I have no problem with this except for the word ‘gewynau’, which the accompanying crib translates as ‘waves’. What is this word? I don’t believe uwch causes a soft mutation, so it seems to be a plural of a word ‘gewyn’, but that appears to mean ‘sinew’, which doesn’t make much sense in the context of a river. So then I thought perhaps uwch can cause a soft mutation, so that would mean it was a plural of the word ‘cewyn’, but this only seems to mean a napkin or a rag, and that makes no sense either. Could it be a plural of one of those tricky Welsh words that change in the middle to make the plural, as well as tacking on an ending? Dunno. Welsh language 1, David 0.
I think it is sinews - I’d say a river can certainly be sinuous (especially in poetry), and, through knowing the Usk at Newport (and a peek on the map will confirm) I’d say it would make sense here.
All I can say is if you can understand everything but that, @Davids, you seem not to need to learn much!
Ah, thank you, I was thinking too literally. What’s the Welsh for poetic licence 
rhyddid bardd! 
Very interesting confluence of meanings here. Gewynau - sinews - sounds like sinuous, but sinuous is from Latin, meaning curvy, and that makes sense in the poem, but sinew is a totally different word with an unrelated meaning. I wonder what is going on.
OK, I’m far from an expert on this, but I understand that there is a Welsh literary device, for which I can’t recall the name. Anyway, its a bit more than alliteration as it also involves some internal rhyme and rhythm. So, the juxtaposed term “gewynau gwinau” might fit this bill (?)
Going back to the Usk at Newport, As Siaron mentioned, the river can look sinuous, or its silted banks at low tide can, complete with water runs. Also it meanders through Newport and has the odd wave now and again.
I love that bit of river, as it is one of the few stretches in the UK that has been allowed to retain its industrial tidal appearance.
The device you mention is cynghanedd, John. There are various types all with particular rules. “gewynau gwinau” (with its repetition of the consonants g and n) would certainly fit certain patterns of the meters.
This will give you a better basic understanding than I could explain myself - https://en.wikipedia.org/wiki/Cynghanedd
That’s brilliant thanks, Siaron. I was just thinking of Dylan Thomas’s introduction to Under Milk Wood, especially this -
“down to the sloeblack, slow, black, crowblack, fishingboat-bobbing sea.”
Yes, although DT didn’t speak Welsh himself, others around him did and he’d certainly have been used to hearing cynghanedd patterns, so - subconsciously if not consciously - it was bound to have had some influence.
I’ve worked/studied/socialised with quite a few prifeirdd, but using cynghanedd I’ve only ever managed one reasonable couplet in Welsh and a poem in English! 
I know Gerard Manley Hopkins was very interested in cynghaneddd and I have wondered if lines like ‘Though worlds of wanwood leafmeal lie’, from his beautiful poem ‘Spring and Fall’, might show its influence. But I’d better not try to pose as an expert on Welsh prosody just yet; I know Aran’s latest email to me urges me to set goals but at the moment I’m preoccupied with getting my tongue round such key phrases as ‘Mae’n ddrwg i fi ond alla i ddim siarad Cymraeg yn dda iawn eto’, and wondering what the Welsh is for ‘Listen, bach, that may be your idea of ‘araf’ but it’s not mine’.