Curse most wicked clients (9)
I believe the answer is:
customers
'clients' is the definition.
('customer' can be a synonym of 'client')
'curse most wicked' is the wordplay.
'wicked' is an anagram indicator.
'curse'+'most'='cursemost'
'cursemost' is an anagram of 'CUSTOMERS'.
(Other definitions for customers that I've seen before include "They're always right, it's said" , "Clientele" , "They pay for goods and services" , "Shop's clients" , "They might buy" .)