Arab megalomaniac's not all there (5)

I believe the answer is:

omani

'arab' is the definition.
(Omani is an example)

'megalomaniac's not all there' is the wordplay.
'not all there' indicates a hidden word (only some of the letters are to be retained).
'OMANI' is hidden within 'megalomaniacs'.

(Other definitions for omani that I've seen before include "Gulf native" , "Eg, a native of Muscat" , "Middle Easterner" , "Naomi (anag) -- from Muscat?" , "Gulf Arab" .)

I've seen this clue in The Telegraph.

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