cerulean(n = noun.attribute) azure, lazuline, sapphire, sky-blue - a light shade of blue;
is a kind of blue, blueness
Derived form adjective cerulean₁

   cerulean(s = adj.all) azure, bright blue, sky-blue - of a deep somewhat purplish blue color similar to that of a clear October sky; "October's bright blue weather"
Derived form noun cerulean₁

   Sky-colored; blue; azure. Cowper. [1913 Webster]
"Blue, blue, as if that sky let fall" [1913 Webster]
"A flower from its cerulean wall." [1913 Webster]

cerulean, adj. & n. literary
--adj. deep blue like a clear sky.
--n. this colour.

Etymology:
L caeruleus sky-blue f. caelum sky

N  blueness, blue, garter-blue, watchet, ultramarine, smalt, cobalt, cyanogen, Prussian blue, syenite blue, bice, indigo, zaffer, lapis lazuli, sapphire, turquoise, indicolite, blueness, bluishness, bloom, blue, azure, cerulean, sky-blue, sky-colored, sky-dyed, cerulescent, powder blue, bluish, atmospheric, retiring, cold.

cerulean blue