Crossword Genius

Go pale, threatening appearance at club (9)

Ross

I believe the answer is:

discolour

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'go pale' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how they can define each other.

'threatening appearance at club' is the wordplay.
'threatening appearance' becomes 'lour' (I've seen this before).
'at' means one lot of letters go next to another (I've seen this in other clues).
'club' becomes 'disco' (night club).
'lour' put after 'disco' is 'DISCOLOUR'.

Can you help me to learn more?

(Other definitions for discolour that I've seen before include "remove shades" , "tarnished" , "fox?" , "Fade - stain" .)

I've seen this clue in The Guardian.
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