Keen on rum being drunk (5)
I believe the answer is:
mourn
'keen' is the definition.
(I've seen this before)
'on rum being drunk' is the wordplay.
'being drunk' indicates an anagram.
'on'+'rum'='onrum'
'onrum' with letters rearranged gives 'MOURN'.
(Other definitions for mourn that I've seen before include "'Miss'" , "Lament loss" , "Express sadness" , "Show sorrow for loss" , "Show sorrow at death" .)