Some money is secure protected by curse (8)
I believe the answer is:
banknote
'some money' is the definition.
(I've seen this before)
'secure protected by curse' is the wordplay.
'secure' becomes 'knot' (I've seen this before).
'protected by' is an insertion indicator.
'curse' becomes 'bane' (synonyms).
'knot' going inside 'bane' is 'BANKNOTE'.
'is' is the link.
(Other definitions for banknote that I've seen before include "Money" , "Paper cash" , "Monetary quantity" .)