Country genius keeps a horse (7)
I believe the answer is:
bahrain
'country' is the definition.
(Bahrain is an example)
'genius keeps a horse' is the wordplay.
'genius' becomes 'brain' (synonyms).
'keeps' means one lot of letters goes inside another.
'horse' becomes 'h' (synonyms).
'a'+'h'='ah'
'brain' enclosing 'ah' is 'BAHRAIN'.
(Other definitions for bahrain that I've seen before include "Gulf sheikhdom, capital Manama" , "kingdom in Middle East" , "Gulf region?" , "Arab state" , "Arab sheikhdom" .)