A hundred is subtracted from the money, as a deposit (3)
I believe the answer is:
ash
'a deposit' is the definition.
(thesaurus)
'a hundred' is the wordplay.
'hundred' becomes 'sh' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'sh'='ASH'
'is subtracted from the money as' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
(Other definitions for ash that I've seen before include "Residue after burning" , "Get the residue" , "blonde" , "Grey colour" , "Remains of conflagration" .)