Moan perversely about Gulf inhabitant's obsessive single-mindedness (9)
I believe the answer is:
monomania
'obsessive single-mindedness' is the definition.
(I've seen this before)
'moan perversely about gulf inhabitant's' is the wordplay.
'perversely' is an anagram indicator.
'about' is an insertion indicator.
'gulf inhabitant's' becomes 'omani' (I can't explain this - if you can you should give a lot more credence to this answer).
'moan' with letters rearranged gives 'mona'.
'mona' enclosing 'omani' is 'MONOMANIA'.
Can you help me to learn more?
(Other definitions for monomania that I've seen before include "Obsession with one thing" , "Unhealthy preoccupation with one thing" , "Single-minded passion" , "obsessive single-mindedness" .)