Bath perhaps is no longer hot (4)
I believe the answer is:
wash
'bath perhaps' is the definition.
(I know that bath is a type of bathing)
'is no longer hot' is the wordplay.
'is no longer' becomes 'was' (eg if someone 'was' sad, they're no longer sad).
'hot' becomes 'h' (common abbreviation eg on taps).
'was'+'h'='WASH'
(Other definitions for wash that I've seen before include "Scrub" , "Clean with liquid" , "Clean; dilute coat" , "Clean oneself" , "Brush with ink; launder" .)