Word of the Week: cerulean (sə-RŌŌ-lē-ən) Definition (Adjective) Of the colour of the cloudless sky, pure deep blue, azure. Chiefly poetic. In Context "It was July, and rolling waves of heat shimmered beneath a cerulean sky." Justin Marozzi, Baghdad, City of Peace, City Of Blood: A History in Thirteen Centuries, 2014.