A great river, it seems, cannot end in nothing! (3)

I believe the answer is:

nil

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'nothing' is the definition.
(eg nil is zero in football)

I can't explain the remainder of the clue.

(Other definitions for nil that I've seen before include "There's nothing left" , "You get nothing" , "Non-existent" , "Nothing, naught" , "Nothing, zero" .)

I've seen this clue in the Evening Standard.

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