add on

add on (third-person singular simple present adds on, present participle adding on, simple past and past participle added on)

1. (transitive) To incorporate (something extra, often an amount of money) into something else (often a bill).
2. (intransitive) To put an expansion onto a building, usually a home.

add on (plural add ons)

1. Alternative form of add-on

   The manufacturer sold many add ons for the basic camera.

   The secretary offered a typing and copying service for theses, with the option of binding as an add on.

• Dando, Donda