Rider's bone

Rider Rid"er (r[imac]d"[~e]r), n. 1. One who, or that which, rides. [1913 Webster]

2. Formerly, an agent who went out with samples of goods to obtain orders; a commercial traveler. [Eng.] [1913 Webster]

3. One who breaks or manages a horse. --Shak. [1913 Webster]

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. [1913 Webster]

After the third reading, a foolish man stood up to propose a rider. --Macaulay. [1913 Webster]

This [question] was a rider which Mab found difficult to answer. --A. S. Hardy. [1913 Webster]

5. (Math.) A problem of more than usual difficulty added to another on an examination paper. [1913 Webster]

6. [D. rijder.] A Dutch gold coin having the figure of a man on horseback stamped upon it. [1913 Webster]

His moldy money ! half a dozen riders. --J. Fletcher. [1913 Webster]

7. (Mining) Rock material in a vein of ore, dividing it. [1913 Webster]

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. [1913 Webster]

9. (Naut.) The second tier of casks in a vessel's hold. [1913 Webster]

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. [1913 Webster]

11. A robber. [Obs. or Prov. Eng.] --Drummond. [1913 Webster]

{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. [1913 Webster]