the act or process of adding or uniting.

the process of uniting two or more numbers into one sum, represented by the symbol +.

the result of adding.

something added.

a wing, room, etc., added to a building, or abutting land added to real estate already owned.

Chemistry . a reaction in which two or more substances combine to form another compound. ?

in addition to

as well as; besides

In addition to directing the play, she designed most of the scenery.

noun

decrease , deduction , lessening , loss , reduction , shrinkage , subtraction , withdrawal , detraction

noun

accession , adding , adjoining , affixing , annexation , attachment , augmentation , enlargement , extension , inclusion , increasingnotes:an addition is something that , when added , serves simply to augment or extend that to which it has been added , leaving the character of the original unchanged; an addendum forms a separate distinguishable portion of the whole and it first meant \'a thing to be added\' , accessory , accretion , accrual , addendum , additive , adjunct , aggrandizement , annex , appendage , appendix , bonus , boost , commission , dividend , enhancement , expansion , extra , gain , hike , increase , increment , option , profit , raise , reinforcement , rise , supplement , wingnotes:an addition is something that , accruing , computing , counting , enlarging , expanding , increasing , reckoning , summation , summing , tabulating , totaling , totingnotes:an addition is something that , totalization , acquisition , amendment , calculation , codicil , joining , more , postscript , rider , suffix , wing