What might rule out a couple? (7)

I believe the answer is:

neither

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'out a couple?' is the definition.
Both the definition and answer are adverbs. Perhaps there's a link between them I don't understand?

I don't understand the rest of the clue.

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(Other definitions for neither that I've seen before include "In three (anag.)" , "Also not" , "Negative word" , "double negative?" , "Not one thing or the other" .)

I've seen this clue in The Telegraph.

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