Rudely ignore (4)
I believe the answer is:
snub
'rudely ignore' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for snub that I've seen before include "Rebuff with buns" , "Pointedly rebuff" , "Reject greeting or approach" , "'Rebuff, ignore (4)'" , "Give (someone) the cold shoulder" .)