Something tremulous is shaky and quivering, usually from fear or lack of strength. If you're nervous at your first big job interview, your hands might be a little tremulous.
You’ve likely heard the unsteady voice of a person close to tears, or seen the trembling legs of a frightened child — both could certainly be described as tremulous. But you can also use this adjective to describe a statement or action that lacks resolution and courage, or even simply something that's shivering from the cold.