mediator; intermediary; middleman
A person or entity that acts as a go-between, facilitating communication, transactions, or relationships.
He advanced the negotiations as a mediator between the two parties.
I look for properties through a real estate intermediary.
disease vector; carrier
Medical term for an organism that transmits a pathogen from one host to another.
Mosquitoes are known as vectors of malaria.
Compound of 媒介 (ばいかい, 'mediation') + 者 (しゃ, 'person'). The word is transparently derived from its components.