Barman's wife in bed? (6)
I believe the answer is:
lawyer
'barman's' is the definition.
(I've seen this before)
'wife in bed?' is the wordplay.
'wife' becomes 'w'.
'in' means one lot of letters goes inside another.
'bed?' becomes 'layer' (bed is a kind of layer).
'w' inserted inside 'layer' is 'LAWYER'.
(Other definitions for lawyer that I've seen before include "One gives legal advice" , "court worker" , "Legal expert" , "Legal adviser" , "Legal specialist" .)