Definition of "cerulean"

cerulean

/səˈɹuːli.ən/

noun
countable and uncountable, plural ceruleans
1. (countable and uncountable, color) A greenish-blue color.
  Quotations
  For our blues we have the azures and ceruleans, lapis lazulis, the light and dusty, the powder blues, the deeps: royal, sapphire, navy, and marine […]
  2014, William H. Gass, On Being Blue: A Philosophical Inquiry, page 59
2. (countable) Any of various lycaenid butterflies of the genus Jamides.
adjective
comparative more cerulean, superlative most cerulean
1. Sky-blue.
  Quotations
  As far to the west as Monica could see, her world was a sea of fog, […] . Above it arched a cerulean sky; as the sun climbed to the zenith, […] , the fog gradually took on a bluish tinge.
  1920, Peter B. Kyne, chapter II, in The Understanding Heart
  Oh Ramona, if there was only some kind of future / And these cerulean skies / Something in our skies, something in our skies
  1995, “The Hearts Filthy Lesson”, in 1. Outside, performed by David Bowie
  But what you don't know is that that sweater is not just blue, it's not turquoise, it's not lapis, it's actually cerulean. And you're also blithely unaware of the fact that in 2002, Oscar de la Renta did a collection of cerulean gowns. And then I think it was Yves Saint Laurent, wasn't it, who showed cerulean military jackets?
  2006, Aline Brosh McKenna, Lauren Weisberger, The Devil Wears Prada, spoken by Miranda Priestly (Meryl Streep)