What does addition mean?
The definition of addition
Ad*di”tion, n.
Etym: [F. addition, L. additio, fr. addere to add.]

1 The act of adding two or more things together; — opposed to subtraction or diminution. “This endless addition or addibility of numbers.” Locke.
2 Anything added; increase; augmentation; as, a piazza is an addition to a building.
3 (Math.)
That part of arithmetic which treats of adding numbers.
4 (Mus.)
A dot at the right side of a note as an indication that its sound is to be lengthened one half. [R.]
5 (Law)
A title annexed to a man’s name, to identify him more precisely; as, John Doe, Esq.; Richard Roe, Gent.; Robert Dale, Mason; Thomas Way, of New York; a mark of distinction; a title.
6 (Her.)
Something added to a coat of arms, as a mark of honor; — opposed to abatement. Vector addition (Geom.), that kind of addition of two lines, or vectors, AB and BC, by which their sum is regarded as the line, or vector, AC.

Synonyms
— Increase; accession; augmentation; appendage; adjunct.