Don't understand why it's not "dost clust" on the basis that it is a pain (as a noun), then what kind of pain? - an ear pain, so... ear becomes the adjective and therefore follows pain. QED in my brain. (Preparing to be embarrassed..._
The usual expressions are clust dost or pigyn clust. Neither seem to be used the other way round.
tost is an adjective here, so it would normally come after the noun.
pigyn is a noun ('a sharp pain'), so the relationship is a possessive one between two nouns ('pain of an ear' = 'ear pain' = 'ear-ache'), where the 'owner' follows the thing 'owned', as in car Dewi ('the car of Dewi' = 'Dewi's car')
I think it's more like "sore throat" - what kind of throat do you have? A sore one. It's the throat that's a noun and "sore" is the adjective.
And here, you have a "sore ear", as it were....
(Gweiadur glosses tost as "sore; ill; acute".)
Never heard clust tost before. Is it a southern saying? Ive always said pigyn clust.
clust dost seems to be used down here in SE Wales, but you will find both in use in the media and in books and articles, etc. pigyn yn y clust, too. There are probably other dialect variations as well.
What about sâl ? Can it be used in place of tost , as an alternative? Or does it have a different shade of meaning?