A cat in charge at a small level (6)

I believe the answer is:

atomic

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

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for atomic that I've seen before include "Like some clocks" , "Type of energy" , "Like nuclear energy" , "Describing tiny particles" , "Extremely small" .)

I've seen this clue in The Mirror.

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