It's different in a car, if it has a horn (6)
I believe the answer is:
africa
'it has a horn' is the definition.
(as in the Horn of Africa, geographical area)
'it's different in a car if' is the wordplay.
'it's different in' indicates anagramming the letters (I've seen this in other clues).
'a'+'car'+'if'='acarif'
'acarif' is an anagram of 'AFRICA'.
(Other definitions for africa that I've seen before include "Continent (6)" , "Continent S. of Europe" , "Second largest continent" , "Always something new from it (Pliny)" , "RAF and CIA strangely together on the continent" .)