Travelling through capital of Vietnam and Iraq, oddly (3)
I believe the answer is:
via
'travelling through' is the definition.
(I've seen this in other clues)
'capital of vietnam and iraq oddly' is the wordplay.
'capital of' indicates taking the first letters.
'and' is a charade indicator (letters next to each other).
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The initial letter of 'vietnam' is 'v'.
The alternate letters of 'iraq' are 'ia'.
'v'+'ia'='VIA'
(Other definitions for via that I've seen before include "A Roman way" , "By way of - in Latin" , "Going through" , "Passing through" , "Roman road" .)