[n] something added to what you have already; "the librarian shelved the new accessions"; "he was a new addition to the staff"
[n] the act of adding one thing to another; "the addition of flowers created a pleasing effect"; "the addition of a leap day every four years"
[n] the arithmetic operation of summing; calculating the sum of two or more numbers; "the summation of four and three gives seven"; "four plus three equals seven"
[n] a component that is added to something to improve it; "the addition of a bathroom was a major improvement"; "the addition of cinammon improved the flavor"
[n] a suburban area laid out in streets and lots for a future residential area
[n] a quantity that is added; "there was an addition to property taxes this year"; "they recorded the cattle's gain in weight over a period of weeks"