Plaintiff with account copper's heard regularly (7)
I believe the answer is:
accuser
'plaintiff' is the definition.
(a plaintiff makes an accusation in court)
'account copper's heard regularly' is the wordplay.
'account' becomes 'ac' (abbreviation for account).
'copper's' becomes 'Cu's' (chemical symbol).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'heard' are 'er'.
'ac'+'cus'+'er'='ACCUSER'
'with' is the link.
(Other definitions for accuser that I've seen before include "Denouncer" , "One to point the finger" , "Prosecutor" , "origin of charge?" , "One charging" .)