adverb · passing quickly, especially in reference to the passage of time

时间忽忽而过，转眼已是十年。

adverb · in a disappointed, dejected, or frustrated state of mind

遭遇接连的失败后，他感到忽忽不乐。

adverb · in a distracted, absentminded, or preoccupied manner

他整日神情忽忽，仿佛若有所失。