Egghead joins choir, awfully brave! (6)
I believe the answer is:
heroic
'brave' is the definition.
(I've seen this in another clue)
'egghead joins choir awfully' is the wordplay.
'egghead' becomes 'e' (head letter of 'egg').
'joins' is an insertion indicator (inserted letters join the word).
'awfully' is an anagram indicator.
'choir' with letters rearranged gives 'hroic'.
'e' going inside 'hroic' is 'HEROIC'.
(Other definitions for heroic that I've seen before include "Surpassing the ordinary, in courage say" , "Valiant, courageous" , "Very brave and noble" , "Extravagant" , "lion-hearted" .)