Definition of "bist"

Thee bist rayther too much a feelosofer, I be afeard, for me.

1875, Mark Lemon, Henry Mayhew, Tom Taylor, Punch

Lookee, thee bist purty, my love; lookee, thee bist purty: thee hast dove's eyes betwix thy locks; thy locks be like a flock o' ship fur thickedness.

1904, Henry Branch, Cotswold and vale