They may be four or seven (4)

I believe the answer is:

seas

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'seven' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

(Other definitions for seas that I've seen before include "Red and Dead" , "Aegean and Mediterranean, say" , "Red and Black are" , "Bodies of salt water" , "Oceans" .)

I've seen this clue in the Evening Standard.

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