词汇与表达：mediate-intercede-arbitrate-negotiate-arbitrary

mediate
If someone mediates between two groups of people, or mediates an agreement between them, they try to settle an argument between them by talking to both groups and trying to find things that they can both agree to.
intercede
http://www.etthink.com/thread-283633-1-1.html

arbitrate
arbit(r)= to judge 判断
arbiter n. 仲裁人；裁决人
arbit 判断 + er 表名词 → 仲裁人；裁决人
arbitrary adj. 武断的
arbitr 判断 + ary …的 →〔随意的〕判断 → 武断的
If you describe an action, rule, or decision as arbitrary, you think that it is not based on any principle, plan, or system. It often seems unfair because of this.
Arbitrary arrests and detention without trial were common.
随意逮捕和拘留屡见不鲜。
arbitrate v. 仲裁
arbitr 判断 + ate 做 → 仲裁
arbitration n. 仲裁
arbitr 判断 + ation，arbitrate 的名词 → 仲裁
arbitrator n. 仲裁者
arbitr 判断 + ator 表人 → 仲裁者