Under the radar, like a lion as opposed to a leopard (9)

I believe the answer is:

unspotted

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'under' is the definition.
Both the answer and definition are adjectives. Maybe there's an association between them I don't understand?

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

Can you help me to learn more?

(Other definitions for unspotted that I've seen before include "Not made out" , "lying doggo?" , "Hidden" , "completely pure?" , "Surely Dalmatian isn't" .)

I've seen this clue in The Daily Express.

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