nebula [LME] In classical Latin a nebula was a mist, fog, or cloud, and in Middle English it had several medical uses. The modern astronomical use, for the cloudlike appearance of a very distant *galaxy is first recorded in 1718 used by Edmond Halley, after whom the *comet is named. Nebulous [LME] was first used literally of something cloudy, and was not used figuratively for something vague or ill-defined until the early 19th century, while the nebulizer that turns medicine into a cloud that can be breathed in is mid 19th century.