Fantastic business with limitless barrel (7)
I believe the answer is:
bizarre
'fantastic' is the definition.
(thesaurus)
'business with limitless barrel' is the wordplay.
'business' becomes 'biz' (informal term for business).
'with' is a charade indicator (letters next to each other).
'limitless' says to take the centre.
The centre of 'barrel' is 'arre'.
'biz'+'arre'='BIZARRE'
(Other definitions for bizarre that I've seen before include "Outr*" , "Really weird" , "Weird and wonderful" , "Very odd" , "Freakish" .)