Man with morals, principally - or the opposite? (7)
I believe the answer is:
antonym
'the opposite?' is the definition.
('antonym' can be a synonym of 'opposite')
'man with morals principally' is the wordplay.
'man' becomes 'antony' (**).
'with' means one lot of letters go next to another.
'principally' suggests taking the first letters.
The initial letter of 'morals' is 'm'.
'antony'+'m'='ANTONYM'
'or' is the link.
(Other definitions for antonym that I've seen before include "Opposite-meaning word" , "opposing description" , "For villain, hero is one" , "Nick's could be free" , "that means reverse" .)