noun
plural -tions
[noncount] :the act or process of joining something to something else :the act or process of adding something - often + of
[noncount] mathematics :the act or process of adding numbers
[count] :something or someone more that is included :something or someone that is added
usually + to
[count] US :a part of a building that is built after the original part has been completed
in addition
as something more - used for adding information to a statement
in addition to
along with or together with (something or someone)