Merriam-Webster's Word of the Day for September 11, 2026 is patina. A patina is primarily defined as a green film that develops on copper and bronze due to exposure to moist air. The term also describes a natural shiny or dark surface that forms over time on materials like wood or leather. Furthermore, patina can refer to any thin layer, either physical or metaphorical. An example illustrates this with a statue developing a seafoam green patina over the years. Another example shows a new winery intentionally given a patina of old-world quaintness. The word's origin traces back to the Italian word for a shallow dish, linked to the film forming on copper dishes. English adopted the term for the green film in the mid-18th century. By the 20th century, its meaning expanded to encompass aged surfaces that gain beauty through time and use, like old furniture. Finally, patina came to describe literal or figurative thin layers, such as a patina of grime or respectability.