Mean minister promises to pay (7)
I believe the answer is:
vicious
'mean' is the definition.
(thesaurus)
'minister promises to pay' is the wordplay.
'minister' becomes 'vic' (I am not sure about this - if you are sure you should believe this answer much more).
'promises to pay' becomes 'IOU's' (promises to pay a debt).
'vic'+'ious'='VICIOUS'
Can you help me to learn more?
(Other definitions for vicious that I've seen before include "Malicious - degenerate" , "Strongly spiteful and dangerous" , "Marked by deep ill will" , "Savage and strongly spiteful" , "Cruel, wicked" .)