Truly it's bravery, going without a bra! (4)
I believe the answer is:
very
'truly' is the definition.
(I've seen this in another clue)
'bravery going without a bra' is the wordplay.
'going without' indicates named letters should be taken away.
'bravery' with 'bra' taken out is 'VERY'.
'it's' is the link.
(Other definitions for very that I've seen before include "Sort of light" , "Extremely - light" , "- light is a flare" , "jolly British!" , "Exceedingly" .)