He or she belongs to the breast fleet; i.e. is a Roman catholic; an appellation derived from their custom of beating their breasts in the confession of their sins.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Bread Basket * BreechedNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes