US circus showman that’s one for new element (6)

I believe the answer is:

barium

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'element' is the definition.
(I know that barium is a type of metal)

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

Can you help me to learn more?

(Other definitions for barium that I've seen before include "Umbria (anag.)" , "Content of meal taken before X-ray" , "Substance swallowed to facilitate X-ray" , "Metallic element, Ba" .)

I've seen this clue in The Times.

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