An Etymological Dictionary of Astronomy and Astrophysics

A line drawn through all points on a weather map having the same amount of → cloud cover.

Etymology (EN): From Gk. → iso- + nephos “cloud,” cognate with Pers. nam “humidity, moisture;” Av. napta- “moist,” nabās-câ- “cloud,” nabah- “sky;” Skt. nábhas- “moisture, cloud, mist;” L. nebula “mist,” nimbus “rainstorm, rain cloud;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” from PIE *nebh- “cloud, vapor, fog, moist, sky.”

Etymology (PE): Izoabr, from izo-, → iso-, + abr → cloud.