Not just a French travelling entertainment (6)
I believe the answer is:
unfair
'not just' is the definition.
('unfair' is the opposite to 'just')
'a french travelling entertainment' is the wordplay.
'a french' becomes 'un' ('a' in French).
'travelling entertainment' becomes 'fair' (travelling fair).
'un'+'fair'='UNFAIR'
(Other definitions for unfair that I've seen before include "Foolishness" , "Dirty" , "'Unjust, inequitable (6)'" , "deceitful" , "Swizz!" .)