Contest level over time (5)
I believe the answer is:
event
'contest' is the definition.
(thesaurus)
'level over time' is the wordplay.
'level' becomes 'even' ('even' can be a synonym of 'level'**).
'over' is a charade indicator (letters next to each other).
'time' becomes 't'.
'even'+'t'='EVENT'
(Other definitions for event that I've seen before include "long jump, say" , "one item in programme" , "Significant happening" , "Something going on" , "Happening, incident" .)