What is a prefix for the word advisable?

There isn't a common, single-word prefix that directly modifies "advisable" to create a new word.

However, you could use "un-" to create the opposite meaning: "unadvisable."

You can also use phrases like "highly", "strongly", "not", "slightly", "somewhat", or "barely" before "advisable" to modify the degree of advice.

For example:

* Highly advisable

* Strongly advisable

* Not advisable

* Slightly advisable

* Somewhat advisable

* Barely advisable