In origin the word strop is simply an alternative form of strap, but it is now mainly used in the sense of a flexible rectangular piece of leather or canvas used for sharpening a razor, also known as a razor strop.It may be in the form of a hanging belt or a hand-held paddle. In both cases, as the names suggest, it makes a dreaded implement for punitive use (e.g. spanking), especially if made of leather, like a tawse; antique razor strops are generally heavier. So just to clarify,do I use the rough or smooth side of my leather?