매개가 · 매개를
medium, intermediary; mediation
Example
모기는 여러 질병을 옮기는 매개 역할을 해요.
Mosquitoes act as carriers that spread many diseases.
Word parts
매 go-between+개 between
Literally 'go-between in the middle'.
Good to know
Usually appears as ~의 매개 역할 or as a modifier: 매개 변수 (parameter).