rider

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that rides, especially one who rides horses.
• noun An unrelated provision added to a legislative bill as a means of trying to get the provision adopted along with the bill or to hamper the passage of the bill.
• noun An amendment or addition annexed to a document, of which it is considered to be a part.
• noun Something, such as the top rail of a fence, that rests on or is supported by something else.

from The Century Dictionary.

• noun A gold coin of Henry VI. of England, of the value of four shillings.
• noun One who rides; particularly, one who rides on the back of a horse or other animal; specifically, one who is skilled in horsemanship and the manège.
• noun A mounted reaver or robber.
• noun Formerly, one who traveled for a mercantile house to collect orders, money, etc.: now called a traveler or (in the United States) drummer.
• noun In horticulture, a budded or grafted standard or stock branching from a main or parent trunk or stem.
• noun A knight.
• noun Any device straddling something; something mounted upon or attached to something else.
• noun Anything saddled upon or attached to a record, document, statement, etc., after its supposed completion; specifically, an additional clause, as to a bill in Congress.
• noun In printing, a cylindrical rod of iron which in use rests on the top of an ink-roller, and aids in evenly distributing the ink on this roller.
• noun A supplementary part of a question in an examination, especially in the Cambridge mathematical tripos, connected with or dependent on the main question.
• noun In a snake fence, a rail or stake one end of which rests on the ground, while the other end crosses and bears upon the fence-rails at their angle of meeting, and thus holds them in place. [Local, U. S.]
• noun In mining, a ferruginous veinstone, or a similar impregnation of the walls adjacent to the vein.
• noun One of a series of interior ribs fixed occasionally in a ship's hold, opposite to some of the principal timbers, to which they are bolted, and reaching from the keelson to the beams of the lower deck, to strengthen the frame.
• noun A piece of wood in a gun-carriage on which the side pieces rest.
• noun A gold coin formerly current in the Netherlands: so called from its obverse type being the figure of a horseman.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who, or that which, rides.
• noun engraving Formerly, an agent who went out with samples of goods to obtain orders; a commercial traveler.
• noun One who breaks or manages a horse.
• noun 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.
• noun (Math.) A problem of more than usual difficulty added to another on an examination paper.
• noun A Dutch gold coin having the figure of a man on horseback stamped upon it.
• noun (Mining) Rock material in a vein of ore, dividing it.
• noun (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.
• noun (Naut.) The second tier of casks in a vessel's hold.
• noun 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.
• noun Obs. or Prov. Eng. A robber.
• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun one who rides, often a horse or motorcycle
• noun politics a provision annexed to a bill under the consideration of a legislature, having little connection with the subject matter of the bill
• noun an amendment or addition to an entertainer's performance contract, often covering a performer's equipment or food, drinks, and general comfort requirements
• noun A small, sliding piece of aluminium on a chemical balance, used to determine small weights

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a traveler riding in a vehicle (a boat or bus or car or plane or train etc) who is not operating it
• noun a clause that is appended to a legislative bill
• noun a traveler who actively rides an animal (as a horse or camel)
• noun a traveler who actively rides a vehicle (as a bicycle or motorcycle)