Green’s Dictionary of Slang

1. a person who benefits by ensnaring other people into actions that will harm them.

1654		Mercurius Fumigosus 22 25 Oct.–1 Nov. 187: Of Sodom Ladies and their Trades, / Of their Hectors, and Trappans.
1657		Trappan Trapt, or The true Relation of a Cunning, Cogging, Confident, Crafty, Counterfeit, Cosening and Cheating Knight, alias Knave [title].
a.1661		‘Vanity of Vanities’ in Rump Poems and Songs (1662) II 110: When first the English War began, / His Father was a Court Trepan.
c.1668		‘The Forsaken Maid’s Frolick’ in Ebsworth Roxburghe Ballads (1891) VII:2 380: And therefore all you that are well in your wits, / Beware of Trappans: Maids, look to your Hits.
a.1674		‘The Thief-Ketcher’s Song’ Head Canting Academy (1674) 145: The twelfth a Trapan, if a Cull he does meet, / He nips all his Cole, and turns him i’th’street.
c.1698		B.E. Dict. Canting Crew n.p.: Trapan, c. he that draws in or wheedles a Cull, and Bites him.
c.1700		London-Bawd (1705) 160: I us’d a great deal of Caution with the other Person who was a Trapan.
1734		C. Johnson Hist. of Highwaymen &c. 68: We had cheated so many with a Pretence of a Child, that the younger Fry were afraid to come nigh us, being looked upon by the Town, as no other than a Couple of subtle Trapans.
1754		Scoundrel’s Dict.

2. a trick or snare.

1656		S. Vernon [bk title] The TREPAN being a true relation, full of stupendious variety, of the strange practises of Mehetabel, the wife of Edward Jones, and Elizabeth, wife of Lieutenant John Pigeon, sister to the said Mehetabel [...] wherein is discovered the subtil method whereby they cheated Mr. Wessel Goodwin, a dyar in Southwark, and all his children of a fair estate.
1667		title in Ebsworth Roxburghe Ballads (1891) VII:2 359: Cupid’s Trappan; or, Up the Green Forest.
1672		Wycherley Love in a Wood IV iii: We are still way-lay’d, with Surprizes, Trapans, Dangers, and Murdering dis-appointments.
1678		Narrative of Bloody Murder of Sir. E. Godfrey 12 Oct. 1: The Trepan was effected thus.
1685		G. Meriton In Praise of York-shire Ale 1: Cheating penny Cans, Three Pipes for two pence; and such like Trepans.