Lacking energy, lacking energy, lacking energy (4)

I believe the answer is:

poky

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'lacking' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for poky that I've seen before include "Cramped (informal)" , "Uncomfortably small (room)" .)

I've seen this clue in The Sunday Times and The Times.

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