Valiant energy in new choir (6)
I believe the answer is:
heroic
'valiant' is the definition.
(I've seen this before)
'energy in new choir' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'in' is an insertion indicator.
'new' indicates an anagram.
'choir' is an anagram of 'hroic'.
'e' put inside 'hroic' is 'HEROIC'.
(Other definitions for heroic that I've seen before include "Superhuman (efforts)" , "Showing extreme courage" , "Very brave and noble" , "Supremely courageous and brave" , "Undaunted" .)