An idle, well-fed dependent or loafer.
“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.
It is used also of religions in contempt; see Dryden's Spanish Friar.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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