Main Difference
The main difference between Amendment and Addendum is that the Amendment is a change to a statute or other legal document and Addendum is a addition made to a document following its publication.
Amendment
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 for better. 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.
Addendum
An addendum, in general, is an addition required to be made to a document by its author subsequent to its printing or publication. It comes from the Latin verbal phrase addendum est, being the gerundive form of the verb addo, addere, addidi, additum, “to give to, add to”, meaning “(that which) must be added”. Addenda is from the plural form addenda sunt, “(those things) which must be added”. (See also memorandum, agenda, corrigenda.)
Amendment (noun)
An alteration or change for the better; correction of a fault or of faults; reformation of life by quitting vices.
Amendment (noun)
In public bodies, any alteration made or proposed to be made in a bill or motion that adds, changes, substitutes, or omits.
Amendment (noun)
Correction of an error in a writ or process.
Amendment (noun)
An addition to and/or alteration to the Constitution.
“The First Amendment guarantees freedom of religion, speech, press, assembly, and petition.”
“The Thirteenth Amendment to the United States Constitution abolished slavery.”
Amendment (noun)
That which is added; that which is used to increase or supplement something.
“a soil amendment”
Addendum (noun)
Something to be added; especially text added as an appendix or supplement to a document.
Addendum (noun)
A postscript.
Addendum (noun)
The height by which the tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line.
Addendum (noun)
an item of additional material added at the end of a book or other publication.
Addendum (noun)
the radial distance from the pitch circle of a cogwheel or wormwheel to the crests of the teeth or ridges.