brighteninggerund / present participle Used attributively (e.g., "brightening sky"), so needs its own entry.
Definitions
Serving to make something brighter or more radiant. The brightening agent restored the fabric's original color.
Becoming brighter, lighter, or more cheerful. She walked on under the brightening sky.
brightengerund / present participle Used attributively to describe something that is in the process of becoming brighter or more cheerful.
Definitions
Becoming brighter or livelier. A brightening sky greeted the early risers.