Righteous extra farewell (7)
I believe the answer is:
goodbye
'farewell' is the definition.
(goodbye is a kind of farewell)
'righteous extra' is the wordplay.
'righteous' becomes 'good' (similar in meaning).
'extra' becomes 'bye' (bye is a type of extra in cricket).
'good'+'bye'='GOODBYE'
(Other definitions for goodbye that I've seen before include "Farewell remark" , "parting" , "so long" , "Cheerio" , "Cheers" .)