Russian fighter, traitor in central Greece, to settle abroad (8)
I believe the answer is:
emigrate
'to settle abroad' is the definition.
'russian fighter traitor in central greece' is the wordplay.
'russian fighter' becomes 'MiG' (Russian fighter plane manufacturer).
'traitor' becomes 'rat' (I've seen this before).
'in' indicates putting letters inside.
'central' says to take the centre.
The central letters of 'greece' are 'ee'.
'mig'+'rat'='migrat'
'migrat' put inside 'ee' is 'EMIGRATE'.
(Other definitions for emigrate that I've seen before include "Permanently leave" , "Leave one's country to live elsewhere" , "Gear item (anag.)" , "Move abroad" , "Leave homeland" .)