Back international language (5)
I believe the answer is:
hindi
'language' is the definition.
(Hindi is an example)
'back international' is the wordplay.
'back' becomes 'hind' ('hind' can be a synonym of 'back').
'international' becomes 'i' (abbreviation eg in IMF).
'hind'+'i'='HINDI'
(Other definitions for hindi that I've seen before include "Language derived from Sanskrit" , "tongue" , "An official language of India" , "language many use" , "Ind. Language" .)