1. a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter
Usage: astronomy
2. a clouded spot on the cornea causing defective vision
Usage: medical; archaic

Examples

• The Orion Nebula is one of the brightest nebulae visible to the naked eye.
• Astronomers use powerful telescopes to study distant nebulae.
• The colorful nebula stretched across several light-years of space.
• New stars are often born within the dense regions of a nebula.
• The Hubble Space Telescope captured stunning images of the Eagle Nebula.
• Dark nebulae appear as black patches against the starry background.