Assert head accepts alcoholic drink being returned (9)
I believe the answer is:
predicate
'assert' is the definition.
(predicating is a kind of asserting)
'head accepts alcoholic drink being returned' is the wordplay.
'head' becomes 'pate' (I've seen this before).
'accepts' indicates putting letters inside.
'alcoholic drink being' becomes 'cider' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'returned' shows that the letters should be reversed in order.
'cider' back-to-front is 'redic'.
'pate' enclosing 'redic' is 'PREDICATE'.
Can you help me to learn more?
(Other definitions for predicate that I've seen before include "Word in a sentence that make a statement about the subject" , "base" , "Describes part of a sentence" , "State" , "subject will be given this for sentence" .)