What is a suffix for the word rash?

There isn't a common, widely used suffix specifically for the word "rash." However, depending on the intended meaning, you could potentially use suffixes like:

* -ness: This would emphasize the quality of being rash, resulting in "rashness."

* -ly: This would turn "rash" into an adverb, indicating how something is done (e.g., "rashly acted").

Remember that these are not standard suffixes for "rash," and their use might depend on the context and desired nuance.