Ace, perhaps, losing head and gaining new courage (5)
I believe the answer is:
nerve
'courage' is the definition.
(I know that nerve is a type of courage)
'ace perhaps losing head and gaining new' is the wordplay.
'ace perhaps' becomes 'serve' (tennis term).
'losing head' means to remove the first letter.
'and gaining' is a charade indicator (letters next to each other).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'serve' with its first letter taken off is 'erve'.
'erve' put after 'n' is 'NERVE'.
(Other definitions for nerve that I've seen before include "Steel - bottle - neck" , "Steadiness, courage" , "Courage - impertinence" , "Fibre to carry instructions between brain and body" , "Strand of body tissue" .)