Order rubbish with a little butter to get sent back (6)
I believe the answer is:
diktat
'order' is the definition.
(I've seen this before)
'rubbish with a little butter to get sent back' is the wordplay.
'rubbish' becomes 'tat' (low-quality items or material).
'with' says to put letters next to each other.
'a little butter' becomes 'kid' (baby goat - goats are animals that butt).
'to get sent back' says the letters should be written backwards (I've seen 'gets sent back' mean this).
'kid' reversed gives 'dik'.
'tat' after 'dik' is 'DIKTAT'.
(Other definitions for diktat that I've seen before include "Harsh order given by someone with authority" , "Harsh order or decree" , "Forceful order that must be obeyed" , "Dogmatic statement" , "Undemocratic decree" .)