Joyful five set off (7)
I believe the answer is:
festive
'joyful' is the definition.
(I've seen this before)
'five set off' is the wordplay.
'off' is an anagram indicator.
'five'+'set'='fiveset'
'fiveset' with letters rearranged gives 'FESTIVE'.
(Other definitions for festive that I've seen before include "Gay" , "Jolly" , "Celebratory, joyful" , "Merry" , "Christmassy" .)