Traveller's stomach flipped during arrival (8)
I believe the answer is:
commuter
'traveller's' is the definition.
(commuter is a kind of traveller)
'stomach flipped during arrival' is the wordplay.
'stomach' becomes 'tum' (synonyms).
'flipped' says the letters should be written backwards.
'during' means one lot of letters goes inside another.
'arrival' becomes 'comer' (synonyms).
'tum' backwards is 'mut'.
'mut' placed within 'comer' is 'COMMUTER'.
(Other definitions for commuter that I've seen before include "traveller of some standing, perhaps?" , "Person who travels some distance to his daily work" , "One who travels some distance to work daily" , "Person who regularly travels some distance to work" , "Person travelling some distance to work" .)