Unbeliever elected Castro, say? (7)
I believe the answer is:
infidel
'unbeliever' is the definition.
(I've seen this before)
'elected castro say?' is the wordplay.
'elected' becomes 'in' (in government).
'castro say?' becomes 'Fidel' (Fidel Castro, former president of Cuba).
'in'+'fidel'='INFIDEL'
(Other definitions for infidel that I've seen before include "Unbeliever" , "Non-believer, heretic" , "Person who has no faith, or the wrong one" , "Sceptical" , "Person not operating in good faith" .)