Country tune (for example) popular in retirement (7)
I believe the answer is:
nigeria
'country' is the definition.
(I know that Nigeria is a country)
'tune for example popular in retirement' is the wordplay.
'tune' becomes 'air' (air can mean a piece of music).
'for example' becomes 'e.g.' (short for 'exempli gratia', 'for example' in Latin).
'popular' becomes 'in' ('in' can mean trendy).
'in retirement' says the letters should be written in reverse (retire can mean to go back or backwards).
'air'+'eg'+'in'='airegin'
'airegin' written backwards gives 'NIGERIA'.
(Other definitions for nigeria that I've seen before include "part of Africa" , "W. African country" , "In rage I turn to this country" , "West African country, capital Lagos" , "Country bordered by Benin, Niger, Chad, and Cameroon" .)