Arab shortly heading north (5)
I believe the answer is:
omani
'arab' is the definition.
(someone from Oman)
'shortly heading north' is the wordplay.
'shortly' becomes 'in a mo' (I've seen this before).
'heading north' is a reversal indicator (in a down clue, letters travel north).
'inamo' back-to-front is 'OMANI'.
(Other definitions for omani that I've seen before include "Middle East national" , "Gulf Arab" , "Gulf native" , "Citizen of a country, capital Muscat" , "One from Muscat" .)