Not as much in Wales say (4)
I believe the answer is:
less
'not as much' is the definition.
(similar in meaning)
'in wales say' is the wordplay.
'in' indicates a hidden word.
'LESS' is hidden within 'wales say'.
(Other definitions for less that I've seen before include "In smaller quantity" , "A smaller amount" , "See 12" , "Comparative of 'a little'" , "Fewer in number" .)