ad·di·tion 
/əˈdɪʃən/ noun
plural ad·di·tions /əˈdɪʃən/ noun 1 [noncount] : the act or process of joining something to something else : the act or process of adding something — often + of ▪ The soup was thickened by the addition of cream in the last stage of cooking. ▪ The town welcomed the addition of three new computers to the library. 2 [noncount] mathematics : the act or process of adding numbers
▪ The children learned addition and subtraction. 3 [count] : something or someone more that is included : something or someone that is added
▪ The museum's collection includes several new additions. — usually + to ▪ an addition to the family [=a new member of the family, such as a newborn baby] ▪ The sculpture is the newest addition to the museum's collection. 4 [count] US : a part of a building that is built after the original part has been completed
▪ The addition expands the kitchen and adds a second bathroom.
▪ The children learned addition and subtraction.
▪ The museum's collection includes several new additions. — usually + to ▪ an addition to the family [=a new member of the family, such as a newborn baby] ▪ The sculpture is the newest addition to the museum's collection.
▪ The addition expands the kitchen and adds a second bathroom.
in addition
: as something more — used for adding information to a statement ▪ The city has the largest population in the country and in addition [=also, additionally] is a major shipping port. ▪ Sandwiches were served, and several salads in addition.
in addition to
: along with or together with (something or someone)
▪ In addition to soup, several salads were served. ▪ There were six people at the meeting in addition to me.
▪ In addition to soup, several salads were served. ▪ There were six people at the meeting in addition to me.
