The exact opposite of taxes collected by a northern island (10)
I believe the answer is:
antithesis
'the exact opposite' is the definition.
('antithesis' can be a synonym of 'exact opposite')
'taxes collected by a northern island' is the wordplay.
'taxes' becomes 'tithes' (I can't explain this - if you can you should believe this answer much more).
'collected by' is a charade indicator (letters next to each other) (I've seen this in other clues).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'island' becomes 'is' (geographical abbreviation).
'a'+'n'='an'
'tithes' put after 'an' is 'antithes'.
'antithes'+'is'='ANTITHESIS'
'of' is the link.
Can you help me to learn more?
(Other definitions for antithesis that I've seen before include "Reverse" , "I oppose the suggestion" , "opposing view" , "Contrast between two things" , "Opposition" .)