形容词

1. (声音或动作)震颤的，颤抖的，打战的；（笑容）怯生生的，不自然的
If someone's voice, smile, or actions are tremulous, they are unsteady because the person is uncertain, afraid, or upset.

1. (of the voice) quivering as from weakness or fear

e.g. the old lady's quavering voice
spoke timidly in a tremulous voice

Synonym: quavering