Heroism without support? Absolutely (4)
I believe the answer is:
very
'absolutely' is the definition.
(I've seen this before)
'heroism without support?' is the wordplay.
'heroism' becomes 'bravery' (I've seen this before).
'without' indicates named letters should be taken away.
'support?' becomes 'bra' (a support for the breasts).
'bravery' with 'bra' taken out is 'VERY'.
(Other definitions for very that I've seen before include "Truly" , "Frightfully" , "Extremely, in a high degree" , "Actual; in a high degree" , "Extremely - light" .)