Con men making entrance (4)
I believe the answer is:
door
'entrance' is the definition.
(I know that door is a type of entrance)
'con men' is the wordplay.
'con' becomes 'do' (to 'do' someone could be to con them).
'men' becomes 'or' (Other Ranks: non-commissioned soldiers).
'do'+'or'='DOOR'
'making' is the link.
(Other definitions for door that I've seen before include "Alternative to knocker" , "Barrier to open and close" , "Hinged barrier" , "Usual entrance" , "Entrance barrier" .)