Right scoundrel follows copper, arrested by one (8)
I believe the answer is:
accurate
'right' is the definition.
(similar in meaning)
'scoundrel follows copper arrested by one' is the wordplay.
'scoundrel' becomes 'rat' (rat can mean a nasty person).
'follows' says to put letters next to each other.
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'arrested by' is an insertion indicator (inserted letters are held or arrested).
'one' becomes 'ace' (ace has a value of one in some card games).
'rat' after 'cu' is 'curat'.
'curat' placed within 'ace' is 'ACCURATE'.
(Other definitions for accurate that I've seen before include "Totally correct" , "Correct in all details" , "Meticulous" , "Exactly right" , "not deviating from the truth?" .)