Fool drinks in old bar in Bath (4)
I believe the answer is:
soap
'bar in bath' is the definition.
'soap' can be an answer for 'bath' (thesaurus). I am not certain of the 'bar in' bit.
'fool drinks in old' is the wordplay.
'fool' becomes 'sap' (synonyms).
'drinks in' indicates putting letters inside (inserted letters are drank in).
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'sap' enclosing 'o' is 'SOAP'.
Can you help me to learn more?
(Other definitions for soap that I've seen before include "Washing aid" , "type of TV programme" , "Washing substance" , "Coronation Street?" , "If soft, it's used to flatter" .)