an intermediate agent or agency; a go-between or mediator.

a medium or means.

an intermediate form or stage.

being between; intermediate.

acting between persons, parties, etc.; serving as an intermediate agent or agency

an intermediary power.

noun

agent , broker , channel , connection , cutout , delegate , emissary , entrepreneur , fixer , go-between * , influence , instrument , interagent , interceder , intercessor , intermediate , mediator , medium , middle person , negotiator , organ , vehicle , intermediator , middleman , agency , instrumentality , instrumentation , mechanism , ambassador , arbitrator , referee , umpire