So found in bath, usually (4)
I believe the answer is:
thus
'so' is the definition.
('thus' can be a synonym of 'so')
'in bath usually' is the wordplay.
'in' indicates a hidden word.
'THUS' is hidden within 'bath usually'.
'found' acts as a link.
(Other definitions for thus that I've seen before include "an original Christmas gift" , "Therefore, hence" , "In this way" , "In this manner" , "As a result" .)