However, depending on the context, you could use several words:
General:
* Additional: This is the most common and straightforward option.
* Supplementary: This implies something that is added to complete or enhance something else.
* Augmented: This suggests that something has been increased in size or amount.
* Supplemental: Similar to supplementary, this emphasizes the act of adding something to fill in gaps.
Specific:
* Additive: This refers to something that is added, particularly in a chemical or physical context.
* Plus: This is a more informal adjective, often used in mathematical contexts.
The best choice depends on the specific meaning you want to convey.