BACK'ED,
dead; as He wishes the Senior backed, i.e. He longs to have his Father upon Six Mens Shoulders. His Backs up, a taunting Expression.
· 
· 
Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
The Vulgar Tongue originally collected by Grose, 1811.
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).