New fear breaking out promises to be wicked (9)
I believe the answer is:
nefarious
'be wicked' is the definition.
(similar in meaning)
'new fear breaking out promises' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'breaking out' indicates an anagram.
'promises' becomes 'IOUs' (promises to pay a debt).
'fear' anagrammed gives 'efar'.
'n'+'efar'+'ious'='NEFARIOUS'
'to' is the link.
(Other definitions for nefarious that I've seen before include "Villainous" , "immoral?" , "Extremely wicked" , "Very bad" , "Wicked, criminal" .)