For a moment Harry had the strangest feeling that she wanted to say something to him; She gave him an odd, tremulous look and seemed to teeter on the edge of speech, but then, with a little of her head, she hustled out of the room after he husband and son.
"Holly and phoenix feather," said Ollivander in a tremulous voice.
Dumbledore’s smile was tremulous.
There are no more uses of "tremulous" in the book.
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She spoke timidly in a tremulous voice.
She tried to sound confident, but her voice was tremulous.