Prophet materially united with a sucker! (4)

I believe the answer is:

seer

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'prophet materially' is the definition.
(I know that prophet is a type of diviner)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for seer that I've seen before include "He forecasts" , "Prophet or clairvoyant" , "wise fellow" , "Person of vision" , "Sibyl" .)

I've seen this clue in the Evening Standard.

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