cerulean (adj.)youdaoicibaDictYouDict[cerulean 词源字典]
1660s, with -an + Latin caeruleus "blue, dark blue, blue-green," perhaps dissimilated from caelulum, diminutive of caelum "heaven, sky," which is of uncertain origin (see celestial). The Latin word was applied by Roman authors to the sky, the Mediterranean, and occasionally to leaves or fields. As a noun, from 1756.[cerulean etymology, cerulean origin, 英语词源]