Bath however is upside down (3)
I believe the answer is:
tub
'bath' is the definition.
(synonyms)
'however is upside down' is the wordplay.
'however' becomes 'but' (I've seen this before).
'is upside down' is a reversal indicator.
'but' backwards is 'TUB'.
(Other definitions for tub that I've seen before include "A ranting preacher informally thumps it" , "'Broad, open vessel (3)'" , "Unwieldy vessel" , "Large plant container" , "Clumsy boat" .)