Enormous performance of endless tomfoolery (8)
I believe the answer is:
gigantic
'enormous' is the definition.
(synonyms)
'performance of endless tomfoolery' is the wordplay.
'performance' becomes 'gig' (a gig is a musical concert).
'of endless' means to remove the last letter (I've seen 'endless' mean this).
'tomfoolery' becomes 'antics' (I've seen this before).
'antics' with its final letter taken off is 'antic'.
'gig'+'antic'='GIGANTIC'
(Other definitions for gigantic that I've seen before include "Of very great size" , "Thumping" , "monster" , "Huge, enormous" , "Extremely large" .)