Etymology
Advertisement
gull (n.1)
shore bird, early 15c. (in a cook book), probably from Brythonic Celtic; compare Welsh gwylan "gull," Cornish guilan, Breton goelann; all from Old Celtic *voilenno-. Replaced Old English mæw (see mew (n.1)).
Related entries & more 
Advertisement
gull (n.2)
cant term for "dupe, sucker, credulous person," 1590s, of uncertain origin. Perhaps from verb meaning "to dupe, cheat" (see gull (v.)). Or it is perhaps from (or influenced by) the bird name (see gull (n.1)); in either case with a sense of "someone who will swallow anything thrown at him." Another possibility is Middle English gull, goll "newly hatched bird" (late 14c.), which is perhaps from Old Norse golr "yellow," from the hue of its down.
Related entries & more 
gull (v.)
"to dupe, cheat, mislead by deception," 1540s, earlier "to swallow" (1520s), ultimately from gull "throat, gullet" (early 15c.); see gullet. Related: Gulled; gulling.
Related entries & more 
gullibility (n.)
1782, earlier cullibility (1728), probably from gull (n.2) "dupe, sucker" + -ability.
Related entries & more 
Advertisement
dupe (n.)

"one easily deceived or led astray by false representations," 1680s, from French dupe "deceived person," from duppe (early 15c.), thieves' jargon, perhaps from phrase de huppe "of the hoopoe," an extravagantly crested and reputedly stupid bird. For names of supposedly stupid birds applied to stupid persons, compare booby, goose (n.), gull (n.2) .

Related entries & more 
rook (n.1)

[European crow], Middle English roke, from Old English hroc, from Proto-Germanic *khrokaz (source also of Old Norse hrokr, Middle Dutch roec, Dutch roek, Middle Swedish roka, Old High German hruoh "crow"), probably imitative of its raucous voice. Compare crow (n.), also Gaelic roc "croak," Sanskrit kruc "to cry out." Used as a disparaging term for persons at least since c. 1500, and extended by 1570s to mean "a cheat," especially at cards or dice, also, later "a simpleton, a gull, one liable to be cheated" (1590s). For sense, compare gull (n.2).

Related entries & more 
pigeon (n.)

late 14c., pijoun, "a dove, a young dove" (early 13c. as a surname), from Old French pijon, pigeon "young dove" (13c.), probably from Vulgar Latin *pibionem, dissimilation from Late Latin pipionem (nominative pipio) "squab, young chirping bird" (3c.), from pipire "to peep, chirp," a word of imitative origin. As an English word it replaced culver (Old English culufre, from Vulgar Latin *columbra, from Latin columbula) and native dove (n.). 

The meaning "one easily duped, a simpleton to be swindled" is from 1590s (compare gull (n.2)). Pigeon-hearted (1620s) and pigeon-livered (c. 1600) are "timid, easily frightened." A pigeon-pair (by 1800) are twins of the opposite sex (or family consisting of a boy and a girl only), so called because pigeons lay two eggs, normally hatching a male and a female.

Related entries & more 
skua (n.)
type of predatory gull, 1670s, from Faeroese skugvur, related to Old Norse skufr "seagull, tuft, tassel," and possibly to skauf "fox's tail."
Related entries & more 
molly (n.2)

seabird, 1857, short for mollymawk, mallemuck, from Dutch mallemok, from mal "foolish" + mok "gull."

Related entries & more