How one might start a story about the last 2,000 years? (4)
I believe the answer is:
once
'how one' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
'start a story about the last 2000 years?' is the wordplay.
I cannot really understand how this works, but
'about' could be 'on' (as in a book 'on' a certain topic) and 'on' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'might' acts as a link.
Can you help me to learn more?
(Other definitions for once that I've seen before include "Sometime" , "At some time past" , "... upon a time for the storyteller" , "At a previous time" , "'... bitten, twice shy'" .)