African country about to embrace second religion (5)
I believe the answer is:
islam
'religion' is the definition.
(Islam is an example)
'african country about to embrace second' is the wordplay.
'african country' becomes 'mali' (Mali is an example).
'about' shows that the letters should be reversed in order.
'to embrace' is an insertion indicator.
'second' becomes 's' (common abbreviation).
'mali' backwards is 'ilam'.
'ilam' placed around 's' is 'ISLAM'.
(Other definitions for islam that I've seen before include "Mails to Muslim religion" , "Mails to great eastern religion" , "organised religion" , "Adherents of a religion" , "Faith with five pillars" .)