Source : Webster's Revised Unabridged Dictionary (1913)

Gradually \Grad"u*al*ly\, adv.
   1. In a gradual manner.

   2. In degree. [Obs.]

            Human reason doth not only gradually, but
            specifically, differ from the fantastic reason of
            brutes.                               --Grew.

Source : WordNet®

gradually
     adv : in a gradual manner; "the snake moved gradually toward its
           victim" [syn: {bit by bit}, {step by step}]