1. 工具;器具;用具
    A tool is any instrument or simple piece of equipment that you hold in your hands and use to do a particular kind of work. For example, spades, hammers, and knives are all tools.

    e.g. I find the best tool for the purpose is a pair of shears.
           我发现做这件事最得力的工具是一把大剪刀。

2. 手段;方法
    You can refer to anything that you use for a particular purpose as a particular type of tool .

    e.g. Writing is a good tool for discharging overwhelming feelings…
           写作是宣泄强烈感情的好方法。
    e.g. The video has become an invaluable teaching tool...
           录像已经成为非常有用的教学手段。

3. 受人利用的人;工具;傀儡
    If you describe someone as a tool of a particular person, group, or system, you mean that they are controlled and used by that person, group, or system, especially to do unpleasant or dishonest things.

    e.g. He became the tool of the security services.
           他成了安全部门的工具。

4. (因罢工或抗议而突然)停工，放下工具
    If you say that workers down tools, you mean that they stop working suddenly in order to strike or to make a protest of some kind.

5. (技能、工具和设备等)从事某行当的工具
    The tools of your trade or the tools of the trade are the skills, instruments, and other equipment that you need in order to do your job properly.

    e.g. They're here to learn the tools of their trade from their American colleagues...
           他们来这里向美国同事学习行业技术和技能。
    e.g. Black-leather jackets and tattoos are the standard tools of the trade for heavy-metal musicians.
           黑皮夹克与纹身是重金属乐手的标准行头。