add-on

英文解釋：

名詞 add-on:

1. a component that is added to something to improve it
   同義詞：addition, improver
2. a supplementary component that improves capability
   同義詞：accessory, appurtenance, supplement

動詞 add-on:

1. make an addition
   同義詞：add on
2. add to the very end
   同義詞：append, add on, supplement, affix