The term "sur tax" is commonly used in tax-related discussions, referring to an additional tax imposed on top of the regular tax. However, there are several other words and phrases that can be used interchangeably for this term. Some of these synonyms include "additional tax," "supplementary tax," "extra levy," "surcharge," "incremental tax," and "incremental surcharge." These synonyms can be used to convey the same meaning as "sur tax," depending on the context in which they are used. It's important to understand the nuances of each term and use them appropriately to communicate effectively in tax-related discussions.