An idle, well-fed dependent or loafer.

This was originally a scornful reference to able-bodied people who lived off the charity of an abbey. It was especially scornful when applied to the monks themselves.

"It came into a common proverbe to call him an Abbay-lubber, that was idle, wel fed, a long, lewd, lither loiterer, that might worke and would not."
- The Burnynge of Paules Church, 1563.