ce·ru·le·an (s?-ro?o?l?-?n)adj. Azure; sky-blue.[From Latin caeruleus, dark blue; akin to caelum, sky.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.cerulean (s??ru?l??n) , cerule or ceruleousn (Colours) a. a deep blue colour; azureb. (as adjective): a cerulean sea. [C17: from Latin caeruleus, probably from caelum sky]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ce?ru?le?an (s??ru li ?n) adj., n. deep blue; sky blue; azure. [1660?70;