From Latin 'caeruleus' (sky-blue), probably from 'caelum' (sky) — the colour of the heavens themselves.
From Latin 'caeruleus' (dark blue, blue, blue-green, azure), a word of debated etymology. The traditional derivation connects it to 'caelum' (sky, heaven), making 'caeruleus' literally 'sky-coloured.' An alternative derivation links it to an older form '*caelulum' (diminutive of 'caelum'). Some scholars have proposed a connection to the wax-working term 'cēra' (wax), since certain blue-green tints were associated with wax surfaces. The 'caelum' derivation remains the most
The pigment 'cerulean blue' — a cobalt stannate first synthesized in 1789 by the Swiss chemist Albrecht Höpfner — was not commercially available as an artist's pigment until 1860, when Rowney & Co. in London began selling it. Despite being named with a seventeenth-century English word derived from a classical Latin adjective, the pigment itself is a modern chemical invention that the Romans never possessed.