A last drink for the head on retirement? (8)
I believe the answer is:
nightcap
'a last drink' is the definition.
'head on retirement?' is the wordplay.
'head' becomes 'cap' (both can mean the top of something).
'on' says to put letters next to each other.
'retirement?' becomes 'night' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cap' after 'night' is 'NIGHTCAP'.
'for the' acts as a link.
Can you help me to learn more?
(Other definitions for nightcap that I've seen before include "Last drink before bed" , "attire" , "Patching (anag.)" , "what last drink might be" , "something you get at the eleventh hour?" .)