1. One who, or that which, rides.
2. Formerly, an agent who went out with samples of goods to obtain orders; a commercial traveler.
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. (Macaulay) This [question] was a rider which mab found difficult to answer. (A. S. Hardy)
5. (Science: mathematics) 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. (Science: chemical) rock material in a vein of ore, dividing it.
8. An interior rib occasionally fixed in a ship's hold, reaching from the keelson to the beame of the lower deck, to strengthen her frame.
9. 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.
(Science: medicine) 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.