Cancel a Parisian party (4)
I believe the answer is:
undo
'cancel' is the definition.
(I've seen this before)
'a parisian party' is the wordplay.
'a parisian' becomes 'un' ('a' in French).
'party' becomes 'do' (do can informally mean a party).
'un'+'do'='UNDO'
(Other definitions for undo that I've seen before include "Relax" , "Loosen; annul" , "Open or unfasten" , "Loosen (knot)" , "Remove the wrapping" .)