Mountain in part of Africa (5)
I believe the answer is:
benin
'part of africa' is the definition.
('Benin' is part of 'africa')
'mountain in' is the wordplay.
'mountain' becomes 'ben' (ben is a kind of mountain).
'ben'+'in'='BENIN'
(Other definitions for benin that I've seen before include "Nation" , "West African republic" , "Republic in West Africa" , "East African state" , "Country W. of Nigeria" .)