Source : Webster's Revised Unabridged Dictionary (1913)

Tremulous \Trem"u*lous\, a. [L. tremulus, fr. tremere to
   tremble. See {Tremble}.]
   1. Shaking; shivering; quivering; as, a tremulous limb; a
      tremulous motion of the hand or the lips; the tremulous
      leaf of the poplar.

   2. Affected with fear or timidity; trembling.

            The tender, tremulous Christian.      --Dr. H. More.
      -- {Trem"u*lous*ly}, adv. -- {Trem"u*lous*ness}, n.

Source : WordNet®

tremulously
     adv : in a tremulous manner; "the leaves rustled tremulously in
           the wind"