Dictionary.net

Objectionable party measures, likely to be vetoed on their own merits, which are added to important bills to secure their passage. The first use of the rider, of national importance, was the joining in 1820 of the bill for the admission of Maine to that permitting slavery in Missouri, so as to compel the acceptance of both or neither. These were afterward separated. The Army Appropriation Bill of 1856 had a rider attached prohibiting the employment of Federal troops for the enforcement of territorial law in Kansas. The President signed this measure, but protested against the rider. In 1879 the Democrats in Congress attempted by riders on appropriation bills to bring to an end the Federal interference in Southern politics. President Hayes, by firm use of the veto, dealt a severe blow at this objectionable practice. State Constitutions have frequently prevented it by allowing the Governor to veto separate items in appropriation bills.