to say officially that something, especially an earlier official decision, is no longer to be accepted

His conviction was quashed in March 1986 after his counsel argued that the police evidence was all lies. 他的辩护人举证说明了警方的证据是一派谎言，于是对他的判决于1986年3月被撤销了。

to forcefully stop something that you do not want to happen

The revolt was swiftly quashed by government troops. 叛乱很快就被政府军镇压下去了。

The company moved quickly to quash rumours/speculation that it is losing money. 公司迅速采取行动，平息其亏损的谣言。