Shake one's head seeing litter (6)
I believe the answer is:
refuse
'litter' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for refuse that I've seen before include "Decline to take the rubbish" , "'Deny, turn down (6)'" , "Turn down - rubbish" , "Junk" , "Waste, garbage" .)