What's conjured up by a dreamer may be rum (8)
I believe the answer is:
demerara
'be rum' is the definition.
(I know that demerara is a type of rum)
'what's conjured up by a dreamer' is the wordplay.
'what's conjured up by' indicates anagramming the letters (the answer can be conjured up from the letters).
'a'+'dreamer'='adreamer'
'adreamer' is an anagram of 'DEMERARA'.
'may' is the link.
(Other definitions for demerara that I've seen before include "sweetener" , "Rum" , "That's sweet!" , "Variety of sugar" , "sugar - and alcohol" .)