Fortune to keep after taxes (3)
I believe the answer is:
net
'after taxes' is the definition.
(as in net profits)
'fortune to keep' is the wordplay.
'keep' says the answer is hidden in the clue.
'NET' is hidden in the letters of 'fortune to'.
(Other definitions for net that I've seen before include "Fish-catching mesh" , "Mesh; entrap" , "Open-meshed fabric" , "Trap; open-weave fabric" , "Score a goal" .)