a.

1. 不明确的；含糊的；不确定的
   The date of his departure is uncertain.

   他离开的日期尚未确定。

2. （人对……）不能确信，不确知[Z][F][（+of/about）][+wh-]
   I am still uncertain whether he will come today.

   我仍不能肯定他今天是否会来。

3. 无常的，易变的，靠不住的
   We didn't have the picnic because the weather was uncertain.

   我们没有出去野餐，因为天气变幻莫测。

4. 不稳定的，变动的

adj.

1. not known, reliable, or definite.
2. not completely confident or sure.