The final release for the occasion (5)
I believe the answer is:
event
'the occasion' is the definition.
(I've seen this before)
'the final release' is the wordplay.
'final' indicates one should take the final letters.
'release' becomes 'vent' (vent can mean to release or let out).
The final letter of 'the' is 'e'.
'e'+'vent'='EVENT'
'for' acts as a link.
(Other definitions for event that I've seen before include "Incident, occurrence" , "A noteworthy happening or occurrence" , "major incident" , "Thing that happens" , "400 metres?" .)