Wicked female almost promises to pay hosts (9)
I believe the answer is:
nefarious
'wicked' is the definition.
(similar in meaning)
'female almost promises to pay hosts' is the wordplay.
'female' becomes 'f' (common abbreviation).
'almost' becomes 'near' (near can mean almost or virtually).
'promises to pay' becomes 'IOU's' (promises to pay a debt).
'hosts' means one lot of letters goes inside another (inserted letters are welcomed or hosted).
'near'+'ious'='nearious'
'f' put inside 'nearious' is 'NEFARIOUS'.
(Other definitions for nefarious that I've seen before include "Extremely wicked" , "Very bad" , "Villainous" , "Wicked, criminal" , "immoral?" .)