Rider /(rīd"ẽr)/

Rid·er

Rider

n.
  1. One who, or that which, rides.
  2. Formerly, an agent who went out with samples of goods to obtain orders; a commercial traveler. [Eng.]
  3. One who breaks or manages a horse.
  4. An addition or amendment to a manuscript or other document, which is attached on a separate piece of paper; in legislative practice, an additional clause annexed to a bill while in course of passage; something extra or burdensome that is imposed.
    After the third reading, a foolish man stood up to propose a rider.
    This [question] was a rider which Mab found difficult to answer.
    — A. S. Hardy.
  5. A problem of more than usual difficulty added to another on an examination paper. (Math.)
  6. A Dutch gold coin having the figure of a man on horseback stamped upon it.
    His moldy money ! half a dozen riders.
    — J. Fletcher.
  7. Rock material in a vein of ore, dividing it. (Mining)
  8. An interior rib occasionally fixed in a ship's hold, reaching from the keelson to the beams of the lower deck, to strengthen her frame. (Shipbuilding)
  9. The second tier of casks in a vessel's hold. (Naut.)
  10. A small forked weight which straddles the beam of a balance, along which it can be moved in the manner of the weight on a steelyard.
  11. A robber. [Obs. or Prov. Eng.]

Phrases & Compounds
Rider's bone
a bony deposit in the muscles of the upper and inner part of the thigh, due to the pressure and irritation caused by the saddle in riding.