intermediary
US /ˌɪn.t̬ɚˈmiː.di.ə.ri/
UK /ˌɪn.t̬ɚˈmiː.di.ə.ri/

1.
a person who acts as a link between people in order to try to bring about an agreement or reconciliation; a mediator.
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The diplomat served as an intermediary between the two warring nations.
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She acted as an intermediary in the negotiations.
1.
acting as a link between people or things.
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The internet serves as an intermediary platform for global communication.
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The software provides an intermediary layer between the user and the database.