Unravel anagram? With constant spirit! (8)
I believe the answer is:
armagnac
'spirit' is the definition.
(I've seen this before)
'unravel anagram? with constant' is the wordplay.
'unravel' is an anagram indicator (I've seen 'unravelling' mean this).
'with' is a charade indicator (letters next to each other).
'constant' becomes 'c' (mathematical abbreviation).
'anagram' with letters rearranged gives 'armagna'.
'armagna'+'c'='ARMAGNAC'
(Other definitions for armagnac that I've seen before include "Type of brandy" , "Spirit" , "stronger drink than ale" , "Dry brandy from south-west France" , "A gram can for a French brandy" .)