Syndicate's backer opening show (5)
I believe the answer is:
event
'show' is the definition.
(event can mean a show or exhibition)
'syndicate's backer opening' is the wordplay.
'backer' suggests the final letters.
'opening' becomes 'vent' (a vent is an opening or outlet).
The final letter of 'syndicate' is 'e'.
'e'+'vent'='EVENT'
(Other definitions for event that I've seen before include "Particular happening" , "Something happening" , "riding competition" , "Function" , "A notable occurrence or happening" .)