What term refers to a process caused by gradual degradation over a long time?

The term that accurately describes a process caused by gradual degradation over a long time is 'ageing.' Ageing refers specifically to the progressive changes that occur in materials or systems as they are exposed to the environment or as they experience usage over significant periods. This encompasses a variety of factors, such as chemical changes, mechanical wear, and physical degradation, reflecting a long-term decline in performance or integrity.

While terms like deterioration, oxidation, and corrosion are related to degradation processes, they each have specific meanings that don't fully capture the broad and gradual nature of ageing. Deterioration can imply a general decline but does not necessarily specify a time frame, and it can happen suddenly as well. Oxidation refers specifically to a chemical reaction involving oxygen, which typically occurs over time but is not synonymous with the broader process of ageing. Corrosion specifically involves the deterioration of metals due to a chemical reaction, often with moisture or other environmental factors. Ageing encompasses all of these processes and more, emphasizing the long-term degradation aspect.