Relax in the tub (4)
I believe the answer is:
soak
'relax in the tub' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for soak that I've seen before include "Steep in liquid" , "Douse, drench" , "Steep (in fluid)" , "Immerse in liquid" , "Make thoroughly wet" .)