One island said to be eight (4)

I believe the answer is:

eyot

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'one island' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for eyot that I've seen before include "Small river island" , "Islet found in a river, (especially in England)" , "There's one at Chiswick" , "Fawlty Towers waiter" , "Little island in a river or lake" .)

I've seen this clue in the Evening Standard.

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