Definition of "wap"

Sir, he said, I saw nothing but the waters wap and the waves wan.

1485, Sir Thomas Malory, “How king Arthur commanded to cast his sword Excalibur into the water and how he was delivered to ladies in a barge”, in Le Morte d'Arthur‎, London: MacMillan & Co, published 1919, book 21, chapter 5, page 480

Ben mort, shall you and I heave a bough, mill a ken, or nip a bung, and then we'll couch a hogshead under the ruffmans, and there you shall wap with me, and I'll niggle with you.

1611, Thomas Middleton, “The Roaring Girl”, in Arthur Henry Bullen, editor, The Works of Thomas Middleton‎, volume 4, published 1885, act 5, scene 1, pages 128–129

No gentry mort hath prats like thine, / No cove e'er wap'd with such a one.

1707, John Shirley, “The Maunder's Praise of his Strowling Mort”, in The Triumph of Wit

Liz, he says, why trine for a make, when you can wap for a winne. I'm no dimber mort, I says. Don't ask you to be a swell mollisher, sister, coves want Miss Laycock, don't look at your mug. So I begin to sell my mother of saints.

1988, Timberlake Wertenbaker, Our Country's Good, act 2, scene 1