Definition of "Addition" :

noun: the act of adding one thing to another

"The addition of flowers created a pleasing effect."

noun: the arithmetic operation of summing; calculating the sum of two or more numbers

noun: a component that is added to something to improve it

"The addition of a bathroom was a major improvement."

noun: a suburban area laid out in streets and lots for a future residential area

noun: something added to what you already have

"He was a new addition to the staff."

noun: a quantity that is added

"There was an addition to property taxes this year."