Add-on and More

Add-on noun - Something that is not necessary in itself but adds to the convenience or performance of the main piece of equipment.

More and add-on are semantically related. In some cases you can use "More" instead an adjective phrase "Add-on".

More adjective - Resulting in an increase in amount or number.

Add-on and more are semantically related. Sometimes you can use "Add-on" instead an adjective "More".