I'm in the middle of reading Albion's Seed, and Fisher quotes William Penn in the context of the simplicity of Quaker dress. Penn mentions "shoes and slip-slaps laced with silk or silver lace..." What in the world are slip-slaps? My Google-fu seems to be failing me. Thanks in advance.
This book on Google Books cites the same quotation, but the author parenthetically adds the fact that slip-slaps were slippers. There we go, that was easy!