a person who rides a horse or other animal, a bicycle, etc.

something that rides.

an additional clause, usually unrelated to the main body, attached to a legislative bill in passing it.

an addition or amendment to a document, testament, etc.

any object or device that straddles, is mounted upon, or is attached to something else.

a rail or stake used to brace the corners in a snake fence.

Shipbuilding . any of various members following and reinforcing primary framing members, esp. a plate or timber running along the top of a keel.

Numismatics .

a former gold coin of Scotland, first issued by James III in 1475, whose obverse bears an equestrian figure of the king.

any of several gold or silver coins of the Netherlands bearing the figure of a horseman.

noun

cowboy , driver , gaucho , horseback rider , horseman/woman , passenger , straphanger , suburbanite , traveler , addendum , addition , adjunct , alteration , attachment , clarification , codicil , measure , modification , revision , supplement , amendment , appendix , clause , endorsement , equestrian , equestrienne (female) , horseman , horsewoman , jockey , motorist , postilion