ce ‧ ru ‧ le ‧ an /səˈruːliən, sɪˈruːliən/ BrE AmE ( also ceˌrulean ˈblue ) noun [uncountable] literary
[ Date: 1600-1700 ; Language: Latin ; Origin: caeruleus 'dark blue' , probably from caelum ; ⇨ ↑ celestial ]
a deep blue colour like a clear sky
—cerulean adjective