Itinerant cashier held never-ending dance party (9)
I believe the answer is:
traveller
'itinerant' is the definition.
(I've seen this before)
'cashier held never-ending dance party' is the wordplay.
'cashier' becomes 'teller' (synonyms).
'held' is an insertion indicator.
'never ending' means to remove the last letter.
'dance party' becomes 'rave' (rave is a type of dance event).
'rave' with its last letter taken off is 'rav'.
'teller' enclosing 'rav' is 'TRAVELLER'.
(Other definitions for traveller that I've seen before include "description of Stevenson or his donkey?" , "Nomadic person" , "Rover" , "He trips off" , "Jet-setter" .)