adverb · surreptitious; stealthy; without being noticed

他趁着天还没亮，悄悄地离开了家。

descriptive · quiet; making little or no noise

深夜的校园里悄悄的，没有一点声音。

descriptive · anxious; worried

眼看最后期限快到了，他整天都表现得忧心悄悄。