additionn.[F. addition, L. additio, fr. addere to add.]1. The act of adding two or more things together; -- opposed to subtraction or diminution.(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.()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.()()