Superior one joining up with four others (5,5)

I believe the answer is:

great lakes

This clue could be a double definition.

'superior' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'one joining up with four others' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

(Another definition for great lakes that I've seen is " Erie, Michigan, Huron etc,".)

I've seen this clue in The Times.

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