a.

1. 心情不稳的，喜怒无常的
   It is difficult to predict his reaction because he is so moody.

   他如此喜怒无常，所以很难预知其反应如何。

2. 闷闷不乐的，郁郁寡欢的
   a moody face

   一张郁郁寡欢的脸

adj.

1. given to unpredictable changes of mood, especially sudden bouts of sullenness.
2. giving a poignant or mysterious impression.