"Do you have a sore arm?"
Translation:Oes braich dost gyda chi?
Yes, ailments as in infections, illnesses etc which tend to affect your whole body - ar. But injuries, etc affecting, usually, a particular part of your body - gyda/gan.
- Mae braich/coes/clust dost gen/gyda i. a sore arm/leg/ear
- Mae annwyd/ffliw/'r frech goch arna i - a cold/flu/measles
A good on-line dictionary such as www.gweiadur.com is useful to look up meanings and examples.
Both these words have been mutated. The basic forms are poen and tost (but a good dictionary will let you look up the mutated forms anyway.).
- poen - a noun meaning 'pain' or 'ache', etc.
- tost - in this context, an adjective meaning 'sore' or 'painful', etc.
Both forms are in common use, so it is best to learn both together, really.
You can stick with just one for you own use, though - the version with tost is probably more widespread, so you could stick with that one unless you have a particular reason to choose poen.