Arab very 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' says the letters should be written in reverse (in a down clue, letters go up).
'inamo' reversed gives 'OMANI'.
'very' is the link.
(Other definitions for omani that I've seen before include "Someone from Muscat" , "coming from the Middle East" , "one from the Middle East" , "One from Muscat" , "Middle East national" .)