deadlier , deadliest
If you describe a person or their behaviour as deadly, you mean that they will do or say anything to get what they want, without caring about other people.
The Duchess levelled a deadly look at Nikko.
公爵夫人无所顾忌地瞪了尼克一眼。
A deadly situation has unpleasant or dangerous consequences.
the deadly combination of low expectations and low achievement.
糟糕的是,期望值低,成绩也低。
You can use deadly to emphasize that something has a particular quality, especially an unpleasant or undesirable quality.
deathly
Broadcast news was accurate and reliable but deadly dull.
新闻广播准确、可靠,但极其枯燥。