From The Collaborative International Dictionary of English v.0.48:
Dupe \Dupe\ (d[=u]p), n. [F., prob. from Prov. F. dupe, dube; of
unknown origin; equiv. to F. huppe hoopoe, a foolish bird,
easily caught. Cf. Armor. houp['e]rik hoopoe, a man easily
deceived. Cf. also Gull, Booby.]
One who has been deceived or who is easily deceived; a gull;
as, the dupe of a schemer.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
Dupe \Dupe\, v. t. [imp. & p. p. Duped (d[=u]pt); p. pr. & vb.
n. Duping.] [Cf. F. duper, fr. dupe. See Dupe, n.]
To deceive; to trick; to mislead by imposing on one's
credulity; to gull; as, dupe one by flattery.
[1913 Webster]
Ne'er have I duped him with base counterfeits. --
Coleridge.
[1913 Webster]