A horse goes back across hot country (5)
I believe the answer is:
ghana
'country' is the definition.
(I know that Ghana is a country)
'a horse goes back across hot' is the wordplay.
'horse' becomes 'nag' (term for an old horse).
'goes back' says the letters should be written backwards.
'across' indicates putting letters inside.
'hot' becomes 'h' (abbreviation eg on taps).
'a'+'nag'='anag'
'anag' in reverse letter order is 'gana'.
'gana' enclosing 'h' is 'GHANA'.
(Other definitions for ghana that I've seen before include "West African republic" , "Woody raspberry stem" , "Ah, nag one into going to Africa" , "Its capital is Accra" , "West African country getting independence from the UK in 1957" .)