Language of the Koran (6)
I believe the answer is:
'language of the koran' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for arabic that I've seen before include "Language (by gum!)" , "Gum --, ingredient of glue and incense" , "1 [GCSE]" , "Common language of Middle East" , "Tongue" .)