How do you spell Rowel

Available Definitions:
1)  n. - The little wheel of a spur, with sharp points.
2)  n. - A little flat ring or wheel on horses' bits.
3)  n. - A roll of hair, silk, etc., passed through the flesh of horses, answering to a seton in human surgery.
4)  v. t. - To insert a rowel, or roll of hair or silk, into (as the flesh of a horse).