Note, celebration involves one displaying finery (7)
I believe the answer is:
regalia
'finery' is the definition.
(synonyms)
'note celebration involves one' is the wordplay.
I cannot quite understand how this works, but
'note' could be 're' (as in do-re-mi) and 're' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'celebration' could be 'gala' (gala is a kind of celebration) and 'gala' is located in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'displaying' is the link.
Can you help me to learn more?
(Other definitions for regalia that I've seen before include "Royal trappings" , "Array" , "Badges of office" , "Crown jewels" , "Insignia of royalty or office" .)