Earl opening contest (5)
I believe the answer is:
event
'contest' is the definition.
(thesaurus)
'earl opening' is the wordplay.
'earl' becomes 'e'.
'opening' becomes 'vent' (vent is a kind of opening).
'e'+'vent'='EVENT'
(Other definitions for event that I've seen before include "Fixture" , "A thing taking place" , "Particular happening" , "Something that takes place" , "A notable occurrence or happening" .)