barnard, n. — Green’s Dictionary of Slang

barnard n.

[SE berner, one who waits with a relay of hounds to intercept a hunted animal]

(UK Und.) that member of a team of swindlers who poses as an independent individual, ostensibly having no knowledge of his new companions but keenly ready to befriend the victim and often pretending to be drunk.

1552		G. Walker Detection of Vyle and Detestable Use of Dice Play 39: While the street and company gather to the fray [...] the barnard steals away with all the stuff.
1591		Greene Notable Discovery of Coosnage in Grosart (1881–3) X 10: As they are set, comes in the Barnard, stumbling into your companie, like some aged Farmer of the Countrey, a straunger unto you all, that had been at some market Towne thereabout, buying and selling, and there tipled so much Malmesie that he has neuer a ready woord in his mouth, and is so carelessse of his money.
1602		W. Watson Quodlibets Religion and State 61: Practicall science inuented by fig-boyes, and men of the Bernard high lawe.
1608		Dekker Belman of London F1: The Barnard is the chiefe Player, for hee counterfeites many parts in one, and is now a drunken man, anon in another humour, and shifts himself into so many shapes, only to blind the Cozen.

In compounds

barnard’s law (n.) [law n. (1)]

(UK Und.) a form of card-sharping in which a team of four con-men fleece a victim.

1552		G. Walker Detection of Vyle and Detestable Use of Dice Play 37: Another oily shift, and for the subtyl invention and fitness of wit exceedeth far all the rest, is the barnard’s law: which, to be exactly practised, asketh four persons at least, each of them to play a long several part by himself.
1591		Greene Notable Discovery of Coosnage in Grosart (1881–3) X 9: There was before this many yeeres agoe a practise pit in use by such shifting companions, which was called the Barnards law, wherein as in the arte of Cunny-catching, four person were required to perfourm their cosning commodity. The taker-vp, the Verser, the Barnard and the Rutter.
1608		Dekker Belman of London F: Maintaining themselues onely by the cozenage they vse in Carde-playing: which kind of play of theirs, they call The Barnards Law.