1. A reference to bioluminescent organisms emitting light during darkness: When the black cat crossed the garden at night, it appeared as if two bright green, noctilucent balls were walking across the garden because no one could see her body but just her gleaming eyes.
2. A term used to describe high clouds that are visible at night: Standing on the hilltop at sunset, people could see the noctilucent clouds flowing eastward ahead of the wind.