American aboard a new train, one coming from Vienna? (8)
I believe the answer is:
austrian
'from vienna?' is the definition.
(I've seen this in another clue)
'american aboard a new train one' is the wordplay.
'american' becomes 'US' (United States).
'aboard' is an insertion indicator.
'a new' indicates anagramming the letters.
'one' becomes 'a' (a thing is one thing).
'train'+'a'='traina'
'traina' is an anagram of 'atrian'.
'us' inserted within 'atrian' is 'AUSTRIAN'.
'coming' is the link.
(Other definitions for austrian that I've seen before include "Hot spicy pod" , "European in an Asian rut" , "person from Europe" , "Person from Vienna, say" , "Hitler's nationality pre-1925" .)