“One gets half the amount”, I put in (4)
I believe the answer is:
unit
'one' is the definition.
('unit' can be a synonym of 'one')
'half the amount i put in' is the wordplay.
'half' means to take half the letters.
'put in' is an insertion indicator.
'amount' cut in half is 'unt'.
'unt' placed around 'i' is 'UNIT'.
'gets' is the link.
(Other definitions for unit that I've seen before include "Piece of furniture" , "Separate part" , "One - kitchen cabinet" , "Single person - group of people" , "Any division of quantity accepted as a standard of measurement" .)