a.

1. 心情不穩的，喜怒無常的
   It is difficult to predict his reaction because he is so moody.

   他如此喜怒無常，所以很難預知其反應如何。

2. 悶悶不樂的，鬱鬱寡歡的
   a moody face

   一張鬱鬱寡歡的臉

adj.

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