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
• arcane
• cryptic
• dark
• deep
• Delphic
• double-edged
• elliptical
• elliptic
• enigmatic
• enigmatical
• equivocal
• fuliginous
• inscrutable
• murky
• mysterious
• mystic
• obscure
• occult
• opaque

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

One of his other child costars was a little more nebulous — the mouse brother Stuart Little. —Victoria Edel, People.com, 4 Feb. 2025

There are also more nebulous items, such as advice to beware of social engineering and watch out for spam. —PCMAG, 22 Jan. 2025

The combination of folkloric illustrations with real images of nebulae makes this, well, nebulous topic more understandable and relatable. —Kayla Randall, Smithsonian Magazine, 4 Dec. 2024

That’s a bit of a nebulous proposition, so here are some guidelines: 1. —Justin Curto, Vulture, 3 Feb. 2025

Word History

Etymology

Latin nebulosus misty, from nebula

First Known Use

1674, in the meaning defined at sense 1

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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