Is lacking compassion over those in deadlock (4)

I believe the answer is:

cold

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'is lacking compassion' is the definition.
(I've seen this in another clue)

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

Can you help me to learn more?

(Other definitions for cold that I've seen before include "Mild viral infection, very common" , "Stand-offish" , "Chill" , "Unemotional; infection" , "At low temperature" .)

I've seen this clue in The Irish Times.

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