"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) .
"to deceive, trick, mislead by imposing on one's credulity," 1704, from dupe (n.). Related: Duped; duping.