noun
arbitrator; mediator; person who settles a dispute
Refers to a person who steps in to resolve a conflict or argument, often in a group setting. Can be used in both formal and informal contexts.
会議で意見が対立したとき、彼が留め役を買って出た。
When opinions clashed at the meeting, he stepped in as the arbitrator.
子供たちの喧嘩に、いつも姉が留め役になる。
The older sister always acts as the mediator in the children's fights.
Compound of 留め (tome, 'stopping') + 役 (yaku, 'role'). Literally 'the role of stopping', referring to a person whose function is to halt or settle disputes.