Cut off tail of pollack, food fish served up (4)
I believe the answer is:
dock
'cut off' is the definition.
(thesaurus)
'tail of pollack food fish served up' is the wordplay.
'tail of' says to take the final letters.
'food fish' becomes 'cod' (I've seen this before).
'served up' is a reversal indicator.
The final letter of 'pollack' is 'k'.
'k'+'cod'='kcod'
'kcod' written backwards gives 'DOCK'.
(Other definitions for dock that I've seen before include "Antidote to nettle stings" , "Use this for nettle stings" , "Court enclosure; plant" , "In court, a prisoner stands in it" , "Where the accused stands in court" .)