Lots of money including marks, shillings (4)
I believe the answer is:
bomb
'lots of money' is the definition.
'including marks shillings' is the wordplay.
'including' indicates putting letters inside.
'marks' becomes 'm' (former German currency).
'shillings' becomes 'bob' (plural as in 'two bob').
'm' put into 'bob' is 'BOMB'.
(Other definitions for bomb that I've seen before include "(Of a theatre production) fail badly" , "Big bucks - flop" , "Unpleasant surprise" , "Explosive device" , "not to be hit!" .)