From WordNet (r) 2.0 (August 2003) [wn]:
gradually
adv : in a gradual manner; "the snake moved gradually toward its
victim" [syn: bit by bit, step by step]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Gradually \Grad"u*al*ly\, adv.
1. In a gradual manner.
[1913 Webster]
2. In degree. [Obs.]
[1913 Webster]
Human reason doth not only gradually, but
specifically, differ from the fantastic reason of
brutes. --Grew.
[1913 Webster]