1. 无害的;（尤指对健康）不造成伤害的
    Something that is harmless does not have any bad effects, especially on people's health.

    e.g. Industry has been working at developing harmless substitutes for these gases...
           该行业一直在努力开发一些可以替代这些气体的无害物质。
    e.g. This experiment was harmless to the animals.
           这个试验不会对动物造成伤害。

2. 无关紧要的;不讨人厌的;不会惹麻烦的
    If you describe someone or something as harmless, you mean that they are not important and therefore unlikely to annoy other people or cause trouble.

    e.g. He seemed harmless enough...
           他看起来不会惹什么麻烦。
    e.g. I would not want to deny them a harmless pleasure.
           我不想剥夺他们这点无伤大雅的乐趣。