Man accepts alternative spirits (6)
I believe the answer is:
morale
'spirits' is the definition.
(thesaurus)
'man accepts alternative' is the wordplay.
'man' becomes 'male' (**).
'accepts' means one lot of letters goes inside another.
'alternative' becomes 'or'.
'male' enclosing 'or' is 'MORALE'.
(Other definitions for morale that I've seen before include "Mood" , "Self-confidence" , "Confidence, sense of wellbeing" , "State of a group's confidence and spirit" , "Degree of optimism (of troops, perhaps)" .)