Negative effect of returning to the North (3)
I believe the answer is:
not
'negative effect' is the definition.
'not' can be an answer for 'negative' (I've seen this in another clue). I'm not certain of the 'effect' bit.
'returning to the north' is the wordplay.
'returning' says the letters should be written backwards.
'the north' becomes 'N' (abbreviation).
'to'+'n'='ton'
'ton' backwards is 'NOT'.
'of' is the link.
Can you help me to learn more?
(Other definitions for not that I've seen before include "Negation of what follows" , "A negative word" , "Type of logic gate" , "Having close-cut hair" , "It negates a word" .)