from The American Heritage® Dictionary of the English Language, 4th Edition
- n. One thing added as a supplement to another.
- n. Computer Science See add-in.
- n. Computer Science A hardware device, such as an expansion card, that is added to a computer to increase its capabilities.
- n. An additional amount or charge.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Something which can be appended to something else.
- n. A software extension or hardware peripheral that provides additional functions or customization for a core application or system.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a component that is added to something to improve it
- n. a supplementary component that improves capability
add + on (Wiktionary)