n.

1. 加，附加[U][（+to）]
   The addition of fruit makes the cereal taste good.

   加了水果使谷类食品变得可口。

2. 【数】加法[U]
   do addition and subtraction

   做加减法

3. 增加的人（或物）；（房屋的）增建部分[U][（+to）]
   The baby is a new addition to our family.

   这个婴儿是我们家新增的人丁。

n.

1. the action or process of adding.
   ▸a person or thing added.
2. the process of adding numbers or amounts.
   ▸Mathematics  the process of combining matrices, vectors, or other quantities under specific rules to obtain their sum or resultant.