What is Amendment?

Legal Definition
An amendment is a formal or official change made to a law, contract, constitution, or other legal document. It is based on the verb to amend, which means to change. Amendments can add, remove, or update parts of these agreements. They are often used when it is better to change the document than to write a new one.
-- Wikipedia
Legal Definition
Legislation. An alteration or change of something proposed in a bill.

2. Either house of the legislature has a rigt to make amendments; but, when so made, they must be sanctioned by the other house before they can become a law. The senate has no power to originate any money bills, (q. v,) but may propose and make amendments to such as have passed the House of representatives. Vide Congress; Senate.

3. The constitution of the United States, art. 5, and the constitutions of some of the states, provide for their amendment. The provisions contained in tho constitution of the United States, are as follows: "Congress, whenever two-thirds of both houses shall deem it necessary, shall propose amendments to this constitution, or, on the application of the legislatures of two-thirds of the several states, shall call a convention for proposing amendments, which, in either case, shall be valid, to all intents and purposes, as part of this constitution, when ratified by the legislatures of three-fourths of the several states, or by conventions in three-fourths thereof, as the one or the other mode of ratification may be proposed by Congress: Provided, that no amendment which may be made prior to the year one thousand eight hundred and eight, shall, in any manner, affect the first and fourth clauses in the ninth section of the first article; and that no state, without its consent, shall be deprived of its equal suffrage in the Senate."
-- Bouviers Law Dictionary
Legal Definition
In practice. The correction of an error committed in any process, pleading or proceeding at law or in equity, and which is done either of course or by the consent of parties or upon motion to the court in which the proceeding is pending. 3 Bl. Comm. 407, 448; 1 Tidd, Pr. 696. Hardin v. Boyd, 113 U. S. 756, 5 Sup. Ct 771, 28 L. Ed. 1141. Any writing made or proposed as an improvement of some principal writing. In legislation. A modification or alteration proposed to be made in a bill on its passage, or an enacted law; also such modification or change when made. Brake v. Calli-Bon (C. C ) 122 Fed. 722.
-- Black's Law Dictionary
Legal Definition
A change in an existing statute made by a legislative body. See 46 Ala. 340. Correction of a mistake or error occurring in a judicial proceeding. See 3 Bl. Comm. 406-410.
-- Ballentine's Law Dictionary