nebulous

adjective

neb·​u·​lous ˈne-byə-ləs 

1

: of, relating to, or resembling a nebula : nebular

2

: indistinct, vague

… this nebulous thing called jazz.

—Josef Woodard

… the nebulous region between mere suspicion and probable cause

—W. R. LaFave & J. H. Israel

The plan is too nebulous.

nebulously adverb

nebulousness noun

Did you know?

Nebulous may sound other-worldly—after all, it’s related to nebula, which refers to a distant galaxy or an interstellar cloud of gas or dust—but its mysteriousness is rooted in more earthly unknowns. Both words ultimately come from Latin nebula, meaning “mist, cloud,” and as far back as the 14th century nebulous could mean simply “cloudy” or “foggy.” Nebulous has since the late 17th century been the adjective correlating to nebula (as in “nebulous gas”), but the word is more familiar in its figurative use, where it describes things that are indistinct or vague, as when Jack London wrote of “ideas that were nebulous at best and that in reality were remembered sensations.”

Synonyms

• ambiguous
• cryptic
• obscure
• dark
• vague
• mysterious

Examples of nebulous in a Sentence

These philosophical concepts can be nebulous.

made nebulous references to some major changes the future may hold

Recent Examples on the Web

It’s taken us almost four years to get through three seasons (sort of two), and these ideas are still nebulous and not in production. —Paul Tassi, Forbes.com, 27 June 2025

But the true superpowers of the presidency are more nebulous, but just as significant. —Philip Elliott, Time, 17 June 2025

These unshakable, vaguely nebulous finales are in many ways the key to the remarkable shelf life of Kubrick’s filmography. —Spike Carter, Air Mail, 14 June 2025

The case relates to the treatment of people attempting to reach Europe who were intercepted by the Libyan Coast Guard (LCG) - which is a nebulous entity comprising forces of the Libyan Navy as well as militias and criminal groups - in 2017. —Frey Lindsay, Forbes.com, 17 June 2025

Word History

Etymology

Latin nebulosus misty, from nebula

First Known Use

1674, in the meaning defined at sense 1

Kids Definition

nebulous

adjective

neb·​u·​lous ˈneb-yə-ləs 

1

: of, relating to, or resembling a nebula

2

: not clear or sharp : vague

nebulously adverb

nebulousness noun