Competition still tense (5)
I believe the answer is:
event
'competition' is the definition.
(I've seen this before)
'still tense' is the wordplay.
'still' becomes 'even' (synonyms).
'tense' becomes 't' (abbreviation used in many dictionaries).
'even'+'t'='EVENT'
(Other definitions for event that I've seen before include "'Occurrence, happening (5)'" , "Occasion; sports contest" , "Something going on" , "Happening, incident" , "400 metres?" .)