‖n.; pl. Noctilucae [ L. noctiluca something that shines by night, fr. nox, noctis, night + lucere to shine, lux light. ] 1. (Old Chem.) That which shines at night; -- a fanciful name for phosphorus. [ 1913 Webster ]

2. (Zool.) A genus of marine flagellate Infusoria, remarkable for their unusually large size and complex structure, as well as for their phosphorescence. The brilliant diffuse phosphorescence of the sea is often due to myriads of Noctilucae. [ 1913 Webster ]