Fools around in baths (4)
I believe the answer is:
spas
'baths' is the definition.
(I know this)
'fools around' is the wordplay.
'fools' becomes 'saps' ('sap' can be a synonym of 'fool').
'around' says the letters should be written in reverse.
'saps' reversed gives 'SPAS'.
'in' acts as a link.
(Other definitions for spas that I've seen before include "Mineral springs" , "Health resorts near springs" , "Bath and suchlike" .)