River nominally female (4)

I believe the answer is:

lena

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This could be a double definition.

'river' is the first definition.
(Lena is an example)

'nominally female' is the second definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

Can you help me to learn more?

(Another definition for lena that I've seen is " River of Siberia (4400 km), the world's ninth longest".)

I've seen this clue in the Evening Standard.

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