Nebula
mid 17th century (as a medical term): from Latin, literally ‘mist’.
wiktionary
Borrowed from Latin nebula(“little cloud, mist”). Akin to Ancient Greek νεφέλη(nephélē, “cloud”), German Nebel(“mist, nebula”), Old Norse nifl, Polish niebo(“sky, heaven”).
etymonline
nebula (n.)
mid-15c., nebule "a cloud, mist," from Latin nebula, plural nebulae, "mist, vapor, fog, smoke, exhalation," figuratively "darkness, obscurity," from PIE root *nebh- "cloud."
Re-borrowed from Latin 1660s in sense of "cataracts in the eye;" astronomical meaning "luminous cloud-like patch in the heavens" is from c. 1730. As early as Hershel (1802) astronomers realized that some nebulae were star clusters, but the certain distinction of relatively nearby cosmic gas clouds from distant galaxies (as these are now properly called) was not made until the 1920s, when the latter were resolved into individual stars (and nebulae) using the new 100-inch Mt. Wilson telescope.
