One with obsessive interest in the origin of Arabia translated Koran (6)
I believe the answer is:
anorak
'one with obsessive interest' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'origin of arabia translated koran' is the wordplay.
'origin of' says to take the initial letters.
'translated' is an anagram indicator.
The first letter of 'arabia' is 'a'.
'koran' with letters rearranged gives 'norak'.
'a'+'norak'='ANORAK'
'in the' is the link.
Can you help me to learn more?
(Other definitions for anorak that I've seen before include "Coat (for the boringly obsessive?)" , "Hooded waterproof jacket" , "Casual outerwear" , "good on most figures?" , "Coat - nerd" .)