add-on
nounUK /ˈæd ɒn/
US /ˈæd ɑːn/
Something extra you add to make a thing bigger or better.
The bike came with a basket as an add-on.
OTHER MEANINGS
2. A small piece of software that adds new features to a program.
She installed an add-on to block ads in her browser.
3. An extra part you can buy to go with a main product.
The printer's add-on tray holds more paper.
4. Something added to a plan or service for more money.
The airline charges for add-ons like extra bags.
5. A thing joined onto another thing.
The shed was an add-on to the back of the garage.