means A slight, involuntary shaking or quivering — of the earth, the body, or the voice — often a small sign of something larger underneath.

from From Latin tremor, "a shaking or trembling," from the verb tremere, "to tremble." That same trembling root runs through a whole nervous family of words — tremble, tremulous, and the theatrical tremolo — and is possibly linked to an ancient root meaning to shake or be afraid, the kind of fear that lives in the muscles before it reaches the mouth.