1793 (implied in gullibility), earlier cullibility (1728), probably connected to gull, a cant term for "dupe, sucker" (1594), which is of uncertain origin. It is perhaps from the bird (see gull (n.)), or from verb gull "to swallow" (1530, from O.Fr. goule, from L. gula "throat,"
see gullet); in either case with a sense of "someone who will swallow anything thrown at him." Another possibility is M.E. dial. gull "newly hatched bird" (1382), which is perhaps from O.N. golr "yellow," from the hue of its down.