Source : Webster's Revised Unabridged Dictionary (1913)

Gullible \Gul"li*ble\, a.
   Easily gulled; that may be duped. -- {Gul"li*bii`i*ty}, n.
   --Burke.

Source : WordNet®

gullible
     adj 1: naive and easily deceived or tricked; "at that early age she
            had been gullible and in love" [syn: {fleeceable}, {green}]
     2: easily tricked because of being too trusting; "gullible
        tourists taken in by the shell game"