Crossword Genius

Puff happening — to be one? (6)

Ross

I believe the answer is:

dragon

I'm a little stuck... Click here to teach me more about this clue!

'be one?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'puff happening' is the wordplay.
'puff' becomes 'drag' (synonyms).
'happening' becomes 'on'.
'drag'+'on'='DRAGON'

'to' is the link.

Can you help me to learn more?

(Other definitions for dragon that I've seen before include "Flying monster of Welsh legend" , "Fire-breathing creature slain by St George" , "Mythical fire-breather" , "battleaxe" , "particularly intimidating woman" .)

I've seen this clue in The Times.
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