Lacking energy, lacking energy, lacking energy (4)

I believe the answer is:

poky

I'm a little stuck... Click here to teach me more about this clue!

'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 Times and The Sunday Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.