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.