Girl involves Arab in obsession (9)
I believe the answer is:
monomania
'obsession' is the definition.
(thesaurus)
'girl involves arab' is the wordplay.
'girl' becomes 'mona' (**).
'involves' is an insertion indicator.
'arab' becomes 'omani' (Omani is an example).
'mona' placed around 'omani' is 'MONOMANIA'.
'in' is the link.
(Other definitions for monomania that I've seen before include "Single-minded passion" , "Unhealthy preoccupation with one thing" , "Obsession with one thing" , "obsessive single-mindedness" .)