What does the prefix in- mean as in words incredible or insoluble?

The prefix "in-" in words like "incredible" and "insoluble" means "not" or "the opposite of".

Here's a breakdown:

* Incredible: Not credible, unbelievable.

* Insoluble: Not soluble, unable to be dissolved.

It's important to note that "in-" can also mean "in" or "into" in some words (e.g., "inward," "inside"). However, in the context of words like "incredible" and "insoluble," it always signifies negation.