What symptom is specifically characterized by stiffness lasting for hours?

Rheumatoid arthritis is characterized by prolonged stiffness, particularly in the morning or after periods of inactivity, which can last for a few hours. This extended duration of stiffness is typically due to the inflammatory processes that occur with this autoimmune condition. In rheumatoid arthritis, the body's immune system mistakenly attacks the synovium, leading to inflammation that not only causes pain but also contributes to significant morning stiffness that can affect daily activities.

In contrast, osteoarthritis primarily results in stiffness that lasts for a shorter duration, usually less than 30 minutes after periods of rest. Acute arthritis may present with sudden onset pain and swelling but does not typically include the extended morning stiffness associated with rheumatoid arthritis. Gout, while it can cause intense pain and some stiffness, does not have the same duration of stiffness or patterns that are characteristic of rheumatoid arthritis. Thus, the defining symptom when considering stiffness lasting for hours points to rheumatoid arthritis as the most accurate answer.