Crossword Genius

Nasty red wine keeps con warmer at night (9)

Ross

I believe the answer is:

eiderdown

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'warmer at night' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'nasty red wine keeps con' is the wordplay.
'nasty' indicates an anagram (a nasty or wrong spelling).
'keeps' indicates putting letters inside (inserted letters are kept inside).
'con' becomes 'do' (to 'do' someone could be to con them).
'red'+'wine'='redwine'
'redwine' with letters rearranged gives 'eiderwn'.
'eiderwn' going around 'do' is 'EIDERDOWN'.

Can you help me to learn more?

(Other definitions for eiderdown that I've seen before include "Warm bedcover" , "I wondered about this warm bed covering" , "what may be on tonight" , "what ducks have to offer us" , "What might keep one warm" .)

I've seen this clue in The Independent.
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