形容詞 unpredictable:

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

1. In advanced years a man's mind might go back on him at some unpredictable moment.
   上了年紀(jì)的人，腦子有時候會一下子不聽使喚。
2. Irregular in course or behavior; unpredictable.
   不規(guī)律的在過程上或行為上無規(guī)律的; 不可預(yù)測的
3. He is moody and unpredictable.
   他喜怒無常而又捉摸不定。