Say yes when willing to do something (5)

I believe the answer is:

ready

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'willing to do something' is the definition.
I can't judge whether this definition defines the answer.

'say yes' is the wordplay.
'say' becomes 'read' (synonyms).
'yes' becomes 'y'.
'read'+'y'='READY'

'when' acts as a link.

Can you help me to learn more?

(Other definitions for ready that I've seen before include "All set to go" , "Prompt and adequate" , "Fully-prepared" , "Quick" , "for immediate use" .)

I've seen this clue in The Daily Express.

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