To honour debts is questionable (7)
I believe the answer is:
dubious
'questionable' is the definition.
(similar in meaning)
'to honour debts' is the wordplay.
'to honour' becomes 'dub' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'debts' becomes 'IOUs' (promises to pay debts).
'dub'+'ious'='DUBIOUS'
'is' is the link.
Can you help me to learn more?
(Other definitions for dubious that I've seen before include "Arousing suspicion" , "Doubtful, uncertain" , "untrustworthy" , "Sceptical, doubtful" , "Open to suspicion" .)