Welshman from Snowdonia done over (3)
I believe the answer is:
dai
'welshman' is the definition.
(Welsh name)
'from snowdonia done over' is the wordplay.
'from' indicates the answer is hidden within the clue.
'over' says the letters should be written backwards.
'iad' is hidden within 'snowdonia done'.
'iad' backwards is 'DAI'.
(Other definitions for dai that I've seen before include "Welshman" , "Welsh male name" , "Perhaps man in Cardiff" , "Welshman's name" , "Lloyd George?" .)