Celebrate holding a show (6)
I believe the answer is:
reveal
'show' is the definition.
('reveal' can be a synonym of 'show')
'celebrate holding a' is the wordplay.
'celebrate' becomes 'revel' (reveling is a kind of celebrating).
'holding' means one lot of letters goes inside another.
'revel' going around 'a' is 'REVEAL'.
(Other definitions for reveal that I've seen before include "Spill beans" , "Final disclosure" , "Make known, uncover and allow to be seen" , "Remove cover, unveil" , "Leak" .)