Alas, taking a fifty per cent cut, therefore, too (4)
I believe the answer is:
also
'too' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for also that I've seen before include "Plus" , "As well, in addition" , "an indication of more to come" , "revolutionary a part for Yugoslavia" , "'Besides, moreover (4)'" .)