unpredictable

形容词 unpredictable:

1. not capable of being foretold
2. unknown in advance
3. not occurring at expected times
   同义词：irregular

1. In advanced years a man's mind might go back on him at some unpredictable moment.
   上了年纪的人，脑子有时候会一下子不听使唤。
2. Irregular in course or behavior; unpredictable.
   不规律的在过程上或行为上无规律的; 不可预测的
3. He is moody and unpredictable.
   他喜怒无常而又捉摸不定。