Give the cold shoulder (4)
I think it could be either:
(Other definitions for shun that I've seen before include "Avoid, keep away from" , "Parade-ground language" , "Steer clear of" , "military command" , "Avoid contact" .)
'give the cold shoulder' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for snub that I've seen before include "Treat with disdain" , "Rude put-down; blunt (nose)" , "Reject greeting, seek to humiliate" , "unusually short" , "put down" .)