1. 致命的;致死的
    If something is deadly, it is likely or able to cause someone's death, or has already caused someone's death.

    e.g. He was acquitted on charges of assault with a deadly weapon.
           他被判用致命武器袭击他人的罪名不成立。
    e.g. ...a deadly disease currently affecting dolphins...
           目前正在威胁海豚生命的致命疾病

2. 为达目的不择手段的;阴险毒辣的;冷酷无情的
    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.

    e.g. His mother's voice was one he knew; ice cold and deadly...
           母亲的声音是他很熟悉的：冰冷、无情。
    e.g. The Duchess levelled a deadly look at Nikko.
           女公爵目光冷峻地盯着尼科。

3. 非常乏味的;极其无聊的
    If you describe someone or something as deadly, you mean that you think they are very dull and boring.

    e.g. She finds these parties deadly.
           她觉得这些聚会无聊极了。

4. (尤用于强调令人不快或不受欢迎的特质) 极其，非常
    You can use deadly to emphasize that something has a particular quality, especially an unpleasant or undesirable quality.

deadly的反义词

    e.g. Broadcast news was accurate and reliable but deadly dull...
           新闻广播准确可靠但却非常枯燥。
    e.g. The north wind was bitter and deadly cold...
           北风寒冷刺骨。

5. 极有害的;破坏性的
    A deadly situation has unpleasant or dangerous consequences.

    e.g. ...the deadly combination of low expectations and low achievement.
           糟糕的是期望值低，收获也低
    e.g. It is here that most students fall into a subtle and deadly trap.
           正是在这一点上大多数学生落入了一个不易察觉但却非常危险的陷阱。

6. (敌人或对手)殊死的，不共戴天的
    Deadly enemies or rivals fight or compete with each other in a very aggressive way.

    e.g. The two became deadly enemies...
           这两人成了死敌。
    e.g. That would make the competition between rival suppliers even deadlier.
           那将使得对立供应商之间的竞争更加你死我活。

7. (运动员或其动作）极富技巧性的，极难防御的
    In sport, deadly players and actions are extremely skilful and successful.

    e.g. ...the fastest and deadliest bowlers in world cricket today.
           当今世界板球界速度最快、最具杀伤力的投手