Green’s Dictionary of Slang

a chance.

1624		Massinger Renegado III iv: It is an euen lay but that you had A Courtier to your Father.
1672		J. Lacy Old Troop V i: It’s an even lay whether this Farce be a Comedy or a Tragedy.
1707		Farquhar Beaux’ Strategem III iii: But I dare not put it upon the lay, for fear of being sent for a soldier.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn).
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.