Unsurpassed as chicken can be? (7)

I believe the answer is:

supreme

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'unsurpassed' is the definition.
(both can mean unbeaten or unbeatable)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for supreme that I've seen before include "Greatest in status, authority or power" , "Chief" , "Most excellent" , "Unrivalled" , "Cardinal, foremost" .)

I've seen this clue in The Sun.

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