Celebration of destiny, say (4)
I believe the answer is:
fete
'celebration' is the definition.
(I know that fete is a type of celebration)
'destiny say' is the wordplay.
'destiny' becomes 'fate' (synonyms).
'say' indicates a 'sounds like' (homophone) clue.
'fate' sounds like 'FETE'.
'of' acts as a link.
(Other definitions for fete that I've seen before include "Outdoor entertainment run for charity" , "Festival; gala" , "Organised outdoor party or charitable event" , "Charity garden party" , "Marilyn Monroe's real first name' constellation" .)