What is "rider's bone"

Rider \Rid"er\ (r[imac]d"[~e]r), 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.
   --Shak.

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.
   --Macaulay.

   This [question] was a rider which Mab found difficult to answer.
   --A. S. Hardy.

5. (Math.) A problem of more than usual difficulty added to another on an examination paper.

6. [D. rijder.] 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. (Mining) Rock material in a vein of ore, dividing it.

8. (Shipbuilding) 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.
   --Totten.

9. (Naut.) The second tier of casks in a vessel's hold.

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.]
    --Drummond.

    Rider's bone (Med.), 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.

n. (context medicine English) 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.