Significant birthday treat's finale, led around yard (6-5)
I believe the answer is:
twenty-first
'significant' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I can't see?
'birthday treat's finale led around yard' is the wordplay.
I cannot really see how this works, but
'yard' could be 'y' (abbreviation) and 'y' is found within the answer.
'led' could be 'wentfirst' (I've seen this in another clue) and 'wentfirst' is found in the leftover letters.
A single letter 't' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for twenty-first that I've seen is " Vernal equinox is around the - of March".)