Just had an email from Aran urging us not to be shy about asking questions, so here goes with my first. I am supplementing the SSiW course work with some listening to Welsh folk songs on You Tube, which is very pleasant but of course you meet some pretty unusual words, or perhaps just unusual spellings, that can prove hard to track down. For example, in the song ‘Ar Lan y Môr’ there is a line ‘Llawn yw’r môr o swnd a chegryn’. Both Wikipedia and the You Tube site translate ‘chegyrn’ as ‘billows’, but is this right? When I look up ‘cegyrn’ on the GPC site it only gives it as a plural of ‘cogwrn’, which in this context would mean limpet or possibly periwinkle.
Yes, I know I should get my priorities right, and periwinkles are unlikely to come up in a typical conversation with a Welsh speaker, but I find it hard to let these things go!
Incidentally would the normal word for sand be ‘tawod’ or is ‘swnd’ just as normal?
It’s chregyn which has mutated following the a. The word without mutation is cregyn - shells. The line translates as " The sea is full of sand and shells" (yes, sand is usually tywod but swnd is a colloquial word for sand in some areas) 
diolch both! The number of times I have heard Ar Lan y Môr without even thinking about exact meanings of the bits I didn’t know by heart!
Diolch yn fawr am eich ateb cyflym.
I love it when the emails work! 
don’t feel guilty anout wanting to know every word. That’s how I am. Don’t like to let any word get past me. In practice, many get past me, but I can’t change my outlook on this. It’s the opposite way to what they tell learners, but otoh, it’s probably better to work with your own nature than against it.