Crossword Genius

Soon to overlook Liberal, about to overlook messenger (8)

Ross

I believe the answer is:

emissary

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'messenger' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

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(Other definitions for emissary that I've seen before include "Person sent to negotiate" , "Someone sent on a mission" , "Diplomat sent on special task" , "Delegate" , "Government messenger" .)

I've seen this clue in The Independent.
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