relating to or causing very serious infectious disease that spreads quickly and kills large numbers of people

Smallpox is clearly the worst of the pestilential diseases. 天花显然是最糟糕的疫病。

In the story, a pestilential fog envelops every population centre in the country. 在这个故事中，全国每一个人口中心都被一种疫病的雾气笼罩着。

full of insects or small animals that are dirty or cause disease

They were sent there from the pestilential slums of New York City. 他们被从纽约漫天蚊虫的贫民窟送到了那里。

They figured it would be a simple matter of digging a few canals through the pestilential swamp and letting its waters pour out to sea. 他们觉得办法很简单，只要在蚊虫滋生的沼泽地挖几条运河让水流到海里就行了。

used to emphasize that you find something unpleasant or annoying

Some pestilential scientist has invented a device that allows parents to trace their child's location via their mobile telephone. 一些极其讨厌的科学家发明了一种设备，可以让父母通过手机追踪孩子的位置。

Part of the delight of Venice is its freedom from the pestilential motor car. 威尼斯的乐趣之一是摆脱了烦人的汽车。