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.
ベクター is the direct loanword for 'vector' in medical and technical contexts, often used interchangeably with 媒介者 in scientific writing.
Compound of 媒介 (ばいかい, 'mediation') + 者 (しゃ, 'person'). The word is transparently derived from its components.