Definition of noctilucent cloud in US English:

noctilucent cloud

noun

  • A high-altitude cloud that is luminous at night, especially in summer in high latitudes.

    • ‘‘Humbug’ refers to natural phenomena such as heavenly bodies, noctilucent clouds, ball lightning, and man-made objects such as glowing blimps.’
    • ‘At these times the clouds are visible and are therefore referred to as noctilucent clouds.’
    • ‘One of them is something that I've never actually seen but I had seen pictures of; it's a thing called a noctilucent cloud, this is a cloud that occurs at about 86 kilometres, it may be present more often than we see it.’
    • ‘Evidence of these changes comes from sightings of noctilucent clouds, very unusual clouds seen only in polar regions and known to be in the mesosphere.’
    • ‘Other terms related to the sky and atmosphere are southern aurora, noctilucent clouds, and one which is now generally familiar, the ozone hole, first noted by British Antarctic Survey scientists working in Antarctica.’

Origin

Late 19th century: from Latin nox, noct- ‘night’ + lucere ‘to shine’ + -ent.

Pronunciation

noctilucent cloud

/näktəˌlo͞os(ə)nt ˈkloud/