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