On reflection, wrong by one new resident (4,2)
I believe the answer is:
live in
'resident' is the definition.
(I've seen this before)
'on reflection wrong by one new' is the wordplay.
'on reflection' shows that the letters should be reversed in order.
'wrong' becomes 'evil' (associated in meaning).
'by' is a charade indicator (letters next to each other).
'one new' becomes 'in' (I've seen this in other clues).
'evil' written backwards gives 'live'.
'live'+'in'='LIVE-IN'
(Other definitions for live in that I've seen before include "Cohabiting" , "Reside at one's place of employment" , "(Of employee or lover) resident" , "Resident at one's place of work" .)