1. A reference to bioluminescent organisms that emit radiance during darkness.
2. Shining by night; as with a noctilucent cloud, a cloud of a kind that occasionally is seen at night in the summer in high latitudes, which occurs in the mesopause (atmosphere) and which some authorities believe is composed purely of cosmic dust and others of ice condensed around cosmic dust particles.
3. Designating or of a luminous cloud of unknown composition, visible at night in the polar regions at an altitude of around 50 miles.

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.