The majority of extra alcohol is spirit (6)
I believe the answer is:
morale
'is spirit' is the definition.
(I've seen this in another clue)
'the majority of extra alcohol' is the wordplay.
'the majority of' means to remove the last letter (most but not all of the word is used).
'extra' becomes 'more' (both can mean additional).
'alcohol' becomes 'ale' (type of beer).
'more' with its final letter removed is 'mor'.
'mor'+'ale'='MORALE'
(Other definitions for morale that I've seen before include "Group spirit and confidence" , "The spirit of a group or individual" , "Strength of purpose" , "Esprit, degree of confidence" , "State of mental confidence" .)