\Rid"er\, 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.