1. 撤销，废止（决定或判决）;宣布无效
If a court or someone in authority quashes a decision or judgment, they officially reject it.

2. 平息，制止，澄清(谣言)
If someone quashes rumours, they say or do something to demonstrate that the rumours are not true.

3. 镇压;压制;平定
To quash a rebellion or protest means to stop it, often in a violent way.

1. put down by force or intimidation

e.g. The government quashes any attempt of an uprising
China keeps down her dissidents very efficiently
The rich landowners subjugated the peasants working the land

Synonym: represskeep downsubduesubjugatereduce

2. declare invalid

e.g. The contract was annulled
void a plea

Synonym: invalidateannulvoidavoidnullify