Down one last rum after dance (12)
I believe the answer is:
disconsolate
'down' is the definition.
(thesaurus)
'one last rum after dance' is the wordplay.
'rum' indicates an anagram (rum can mean strange or unusual).
'after' is a charade indicator (letters next to each other).
'dance' becomes 'disco' (I've seen this before**).
'one'+'last'='onelast'
'onelast' is an anagram of 'nsolate'.
'nsolate' put after 'disco' is 'DISCONSOLATE'.
(Other definitions for disconsolate that I've seen before include "Stuck with the blues" , "Sad; beyond comfort" , "Melancholy" , "Very sad or disappointed" , "Low in spirits" .)