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.

— Increase; accession; augmentation; appendage; adjunct.