Which term refers to a gradual development of a potentially harmful condition?

The term that describes a gradual development of a potentially harmful condition is "insidious." This word is commonly used in medical contexts to refer to diseases or disorders that progress slowly and may not present immediate or obvious symptoms. As a result, the condition can go unnoticed for an extended period, often allowing it to reach a more advanced or harmful stage before a diagnosis is made.

In contrast, "labile" typically refers to something that is unstable or subject to change, often used in relation to emotions or conditions that fluctuate unpredictably. "Intact" means undamaged or whole, which does not convey the notion of development or potential harm. "Latent" refers to a condition that exists but is not currently active or visible; while it does have implications of hidden potential, it does not specifically imply a gradual progression toward harm as "insidious" does. Thus, "insidious" is the most appropriate term to characterize conditions that develop slowly and might lead to adverse effects.