A dreamer desperate for rum (8)
I believe the answer is:
demerara
'for rum' is the definition.
(demerara is a type of rum)
'a dreamer desperate' is the wordplay.
'desperate' indicates an anagram (a desperate or pathetic spelling).
'a'+'dreamer'='adreamer'
'adreamer' anagrammed gives 'DEMERARA'.
(Other definitions for demerara that I've seen before include "(Light-brown) sugar" , "That's sweet!" , "sweetener" , "sugar - and alcohol" , "Light brown cane sugar" .)