Brave egghead in mixed choir (6)
I believe the answer is:
heroic
'brave' is the definition.
(I've seen this in another clue)
'egghead in mixed choir' is the wordplay.
'egghead' becomes 'e' (head letter of 'egg').
'in' indicates putting letters inside.
'mixed' indicates anagramming the letters.
'choir' is an anagram of 'hroic'.
'e' inserted inside 'hroic' is 'HEROIC'.
(Other definitions for heroic that I've seen before include "Undaunted" , "larger than life" , "Imposing or impressive: very courageous" , "Epic" , "Valiant, courageous" .)