add something ↔ on (also add something on something) phrasal verb (see also add)
to include or put on something extra:
proposals to add a penny on income tax
add something ↔ on to
The private chapel was added on to the church much later.

[TahlilGaran] Dictionary of Contemporary English ▲

ˈadd-on noun [countable]

1. something extra that is added to an existing plan, agreement, law etc
add-on to
We bought legal protection as an add-on to our home insurance policy.

2. a piece of equipment that you connect to a computer to improve its performance:
an add-on circuit board

3. a product that is designed to be used with another product

[TahlilGaran] Dictionary of Contemporary English ▲