Immaculate, unlike leopard (8)

I believe the answer is:

spotless

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'immaculate' is the definition.
(I know that immaculate can be written as spotless)

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

Can you help me to learn more?

(Other definitions for spotless that I've seen before include "Without a mark, completely clean" , "Above reproach - perfectly clean" , "Extremely clean" , "Fully clean" , "How Lady Macbeth wanted to be" .)

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