In Wales, an undiluted hogshead (5)
I believe the answer is:
neath
'in wales an' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'undiluted hogshead' is the wordplay.
'undiluted' becomes 'neat' (similar in meaning).
'hogshead' becomes 'h' (head letter of 'hogs').
'neat'+'h'='NEATH'
Can you help me to learn more?
(Other definitions for neath that I've seen before include "River" , "Under (poetic)" , "Town NE of Swansea" , "Under, poetically" , "Lower than - a town in West Glamorgan" .)