add on

n.

a component that is added to something to improve it

同义词：additionadd-onimprover

a supplementary component that improves capability

同义词：accessoryappurtenancesupplementadd-on

1. They decided to add on a new room to the house.
   他们决定给房子加建一个新房间。
2. You can add on extra storage for an additional fee.
   你可以支付额外费用来增加存储空间。