Crossword Genius

One of the four (or seven) sitting next to Ted (3)


I believe the answer is:


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'one' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for sea that I've seen before include "Large body of salt water" , "Watery expanse" , "Adriatic, for example" , "North, say" , "E.g Aral or Weddell" .)

I've seen this clue in the Evening Standard.
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