"No" irrelevant before "yes" (3)

I believe the answer is:

nay

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'no' is the definition.
(archaic form 'no')

'irrelevant before yes' is the wordplay.
'irrelevant' becomes 'na' (I can't justify this - if you can you should believe this answer much more).
'before' means one lot of letters go next to another.
'yes' becomes 'y'.
'na'+'y'='NAY'

Can you help me to learn more?

(Other definitions for nay that I've seen before include "Denial" , "No (dialect); or rather" , "No - a negative vote" , "disagreement" , "Indeed" .)

I've seen this clue in The Independent.

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