The word "unbright" typically refers to something that is dull or lacking in brightness. Some common antonyms for "unbright" include words such as "bright", "vibrant", "luminous", and "radiant". These words describe something that is full of light, energy, and color, and are often used to describe things like sunshine, flowers, and vibrant artwork. Other antonyms for "unbright" might include words like "shiny", "gleaming", "sparkling", or "glowing". These words imply a sense of brightness and clarity, and can be used to describe objects such as polished metal or a bright star in the night sky.