Cowardly to react thus to being hurt? (6)

I believe the answer is:

yellow

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'cowardly' is the definition.
(yellow can informally mean cowardly)

I don't understand how the remainder of the clue works.

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(Other definitions for yellow that I've seen before include "See 15" , "show sign of age" , "Flaxen" , "Chicken-hearted" , "Colour of cowardice, custard" .)

I've seen this clue in The Times.

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