Out putting label on ducks (5)
I believe the answer is:
taboo
'out' is the definition.
(synonyms)
'label on ducks' is the wordplay.
'label' becomes 'tab' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'ducks' becomes 'oo' (I've seen this in other clues).
'tab'+'oo'='TABOO'
'putting' acts as a link.
(Other definitions for taboo that I've seen before include "Forbidden by social custom" , "Not permitted" , "Prohibited, sacred" , "Ritual prohibition" , "Prohibited by social custom" .)