D defs.my
Entry 11 senses Webster, 1913

Rider

/(rīd"ẽr)/ · Rid·er · IPA /ˈɹaɪ.dəɹ/
01 n. One who, or that which, rides.
  1. 1.
    One who, or that which, rides.
  2. 2.
    Formerly, an agent who went out with samples of goods to obtain orders; a commercial traveler.[Eng.]
  3. 3.
    One who breaks or manages a horse.
  4. 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. 5.
    A problem of more than usual difficulty added to another on an examination paper.(Math.)
  6. 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. 7.
    Rock material in a vein of ore, dividing it.(Mining)
  8. 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. 9.
    The second tier of casks in a vessel's hold.(Naut.)
  10. 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. 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.