noun that part of arithmetic which treats of adding numbers.
2. addition ·noun something added to a coat of arms, as a mark of honor;
opposed to abatement.
3. addition ·noun anything added; increase; augmentation; as, a piazza is an addition to a building.
4. addition ·noun the act of adding two or more things together;
opposed to subtraction or diminution.
5. addition ·noun a dot at the right side of a note as an indication that its sound is to be lengthened one half.
6. addition ·noun 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.