Legions’ fermented spirit (4,3)
I believe the answer is:
sloe gin
'spirit' is the definition.
(I've seen this before)
'legions' fermented' is the wordplay.
'fermented' indicates an anagram.
'legions' is an anagram of 'SLOE-GIN'.
(Other definitions for sloe gin that I've seen before include "Alcoholic infusion" , "Liqueur made with blackthorn fruit" , "Blackthorn-fruit flavoured liqueur -- Leo sign (anag)" , "Legions (anag.)" , "tipple" .)