Plaintiff's account primarily compromised client (7)
I believe the answer is:
accuser
'plaintiff's' is the definition.
(thesaurus)
'account primarily compromised client' is the wordplay.
'account' becomes 'ac'.
'primarily' indicates taking the first letters.
'client' becomes 'user'.
The first letter of 'compromised' is 'c'.
'ac'+'c'+'user'='ACCUSER'
(Other definitions for accuser that I've seen before include "One bringing a charge" , "Denouncer" , "he's pointing the finger" , "One to point the finger" , "One imputing guilt" .)