Definition of nacreous cloud in US English:

nacreous cloud

noun

  • An iridescent cloud; (specifically in Meteorology) one of a kind occasionally seen in winter in high latitudes, showing bright colours after sunset, and forming in the stratosphere at a height of 12–18 miles (20–30 kilometres); also called mother-of-pearl cloud.

Origin

Early 20th century. From nacreous + cloud.

Pronunciation

nacreous cloud

/ˈneɪkrɪəs ˌklaʊd/