nacreous cloud

mother-of-pearl cloud noun a luminous iridescent cloud at a high altitude that may be seen when the sun is a few degrees below the horizon
Found on http://wordnetweb.princeton.edu/perl/webwn?s=nacreous%20cloud

Nacreous Cloud

A rare, often coloured, cloud at heights between 15 and 30 km. sometimes called mother of pearl clouds.
Found on http://www.metcheck.com/OTHER/glossary.asp
No exact match found