1. 不稳定的；不可靠的；动荡的
    You can describe something as unstable if it is likely to change suddenly, especially if this creates difficulty or danger.

    e.g. After the fall of Pitt in 1801 there was a decade of unstable government...
           1801年皮特倒台后，政府经历了10年的动荡。
    e.g. The situation is unstable and potentially dangerous.
           情况不稳定，可能有危险。

2. 不牢固的；松脱的
    Unstable objects are likely to move or fall.

unstable在线翻译

    e.g. Both clay and sandstone are unstable rock formations.
           黏土和砂岩都是不牢固的岩石构造。

3. （情绪）不稳定的，波动的
    If people are unstable, their emotions and behaviour keep changing because their minds are disturbed or upset.

    e.g. He was emotionally unstable...
           他情绪不稳定。
    e.g. Coleridge was also a highly unstable person.
           科尔里奇还是个情绪非常不稳定的人。