I can rave, supporting European traveller (9)
I believe the answer is:
itinerant
'traveller' is the definition.
(itinerant is a kind of traveller)
'i can rave supporting european' is the wordplay.
'can' becomes 'tin' (synonyms).
'rave' becomes 'rant' (synonyms).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'european' becomes 'E' (abbreviation e.g. EU).
'rant' after 'e' is 'erant'.
'i'+'tin'+'erant'='ITINERANT'
(Other definitions for itinerant that I've seen before include "Old labourer/traveller who travelled from place to place" , "Tramp" , "Wandering from place to place" , "Travelling around" , "Rambling" .)