1.additional的基本意思是“增加的,额外的,另外的”,指在原有总数的基础上进行了添加,使其成为整体的补充。
2.additional不用于比较等级。

用作定语
▲～+n.
 An additional charge is made for heavy bags.重的行李要额外收费。
Mother needs additional help in the kitchen.母亲还需要人帮厨。
It will take additional two weeks to finish the work.还得花两个星期才能完成这项工作。
▲n.+～
These are things additional.这是一些附加的东西。
用作表语
▲S+be+～+to n./pron.
This problem is additional to their major financial anxieties.这道难题使他们的财政状况更加令人担忧。
This problem is additional to my difficult situation.这一问题加剧了我的困境。