Uniform put on entrant, finally, for competition (5)
I believe the answer is:
event
'competition' is the definition.
(I've seen this before)
'uniform put on entrant finally' is the wordplay.
'uniform' becomes 'even' (I've seen this before).
'put on' says to put letters next to each other.
'finally' indicates one should take the final letters.
The final letter of 'entrant' is 't'.
'even'+'t'='EVENT'
'for' acts as a link.
(Other definitions for event that I've seen before include "Function" , "'Occurrence, happening (5)'" , "High jump, say" , "A notable occurrence or happening" , "Something taking place" .)