(n)addition, add-on, improvera 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”
(n)addition, increase, gaina 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”
(n)summation, addition, plusthe 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”