Whittle down first choice (4-4)

I believe the answer is:

blue-chip

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'choice' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

'whittle down first' is the wordplay.
'whittle' becomes 'chip' (I can't justify this - if you can you should give a lot more credence to this answer).
'down' becomes 'blue' (both can mean sad).
'first' is a charade indicator (letters next to each other).
'chip' after 'blue' is 'BLUE-CHIP'.

Can you help me to learn more?

I've seen this clue in The Independent.

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