Not so fair, challenger trapping king (6)

I believe the answer is:

darker

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'not so fair challenger trapping king' is the definition.
I can't tell whether this defines the answer.

'challenger trapping king' is the wordplay.
'challenger' becomes 'darer' (I've seen this in another clue).
'trapping' indicates putting letters inside.
'king' becomes 'K' (chess abbreviation).
'darer' going around 'k' is 'DARKER'.

Can you help me to learn more?

(Other definitions for darker that I've seen before include "More deficient in light" , "Less illuminated" , "More gloomy" , "Dimmer, murkier" .)

I've seen this clue in The Times.

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