addition, add-on, improver -- (a component that is added to something to improve it; "the addition of a bathroom was a major improvement"; "the addition of cinnamon improved the flavor")
addition -- (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")
addition, increase, gain -- (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")
accession, addition -- (something added to what you already have; "the librarian shelved the new accessions"; "he was a new addition to the staff")
addition -- (a suburban area laid out in streets and lots for a future residential area)
summation, addition, plus -- (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")
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