Second man to entertain bishop in small room? (5)
I believe the answer is:
cabin
'small room?' is the definition.
(small room on a ship)
'second man to entertain bishop' is the wordplay.
'second man' becomes 'cain' (biblical second man after Adam).
'to entertain' means one lot of letters goes inside another.
'bishop' becomes 'B' (chess abbreviation).
'cain' enclosing 'b' is 'CABIN'.
'in' acts as a link.
(Other definitions for cabin that I've seen before include "Wooden shack" , "Small room on a ship" , "Room on board ship" , "Compartment on a ship" , "modest accommodation" .)