Say no to what you don't want (6)
I believe the answer is:
refuse
'say no' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for refuse that I've seen before include "Deny; rubbish" , "Don't take the rubbish" , "Say no to - rubbish" , "Decline to jump; rubbish" , "Pass up" .)