rowel

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A sharp-toothed wheel inserted into the end of the shank of a spur.

from The Century Dictionary.

• To use the rowel on; put spurs to.
• In farriery, to apply a rowel to.
• To furnish with a rowel, as a spur.
• noun . A small wheel, ring, or circle.
• noun The wheel of a horseman's spur, armed with pointed rays.
• noun A roller on the mouthpiece of an old form of bit for horses.
• noun In farriery, a seton inserted in the flesh of an animal.
• noun The spiked wheel of some forms of soil-pulverizers and wheel-harrows.

from the GNU version of the Collaborative International Dictionary of English.

• noun The little wheel of a spur, with sharp points.
• noun A little flat ring or wheel on horses' bits.
• noun (Far.) A roll of hair, silk, etc., passed through the flesh of horses, answering to a seton in human surgery.
• transitive verb (Far.) To insert a rowel, or roll of hair or silk, into (as the flesh of a horse).

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The small spiked wheel on the end of a spur.
• verb transitive To use a rowel on something, especially to drain fluid.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a small spiked wheel at the end of a spur