Under; Welsh town (5)
I believe the answer is:
neath
I believe this clue is a double definition.
'under' is the first definition.
(I've seen this in another clue)
'welsh town' is the second definition.
(I've seen this before)
(Other definitions for neath that I've seen before include "Welsh rugby club" , "Town near Swansea" , "not on top" , "Welsh industrial town" , "Under, poetically" .)