Which term describes a process that occurs in a gradual, subtle way but can have harmful effects?

The term "insidious" is used to describe a process that develops gradually and subtly, often in a way that is not immediately noticeable but ultimately leads to harmful consequences. This is relevant in a variety of contexts, including health, behavior, and even environmental issues. For example, certain diseases can progress without obvious symptoms at first, causing serious harm by the time they are detected.

The other terms do not convey the same meaning. "Overt" refers to something that is done openly and is easily observable, while "transparent" suggests clarity and visibility. "Obvious" indicates something that is clear and unmistakable. All of these terms lack the nuanced implication of gradual and hidden danger that "insidious" embodies.