add on

Verb

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

Noun

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