means A vast interstellar cloud of gas and dust, often glowing or dark, where stars are born and where dying stars scatter their material.

from Straight from Latin nebula, meaning 'mist, fog, cloud' — a word for the haze you couldn't quite see through. It's likely related to Greek nephele, also 'cloud,' and shares deep roots with the same family that gave us 'nebulous' for anything vague. Astronomers borrowed it for the faint, fuzzy smudges in the night sky long before telescopes revealed many of them to be distant galaxies or true clouds of cosmic dust.