Learner's definition of ADDITION
1 [noncount] : the act or process of joining something to something else : the act or process of adding something — often + of 2 [noncount], mathematics : the act or process of adding numbers 3 [count] : something or someone more that is included : something or someone that is added — 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
: 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.