Isn't giving them first two original promissory notes, which is disreputable (9)
I believe the answer is:
notorious
'is disreputable' is the definition.
(similar in meaning)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for notorious that I've seen before include "Undesirably well-known" , "of ill-repute" , "Famous for bad deeds" , "Disgraceful" , "Scandalous" .)