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

Back then, the elements that eventually coalesced into the Gateway were geared toward a nebulous initiative to capture a small asteroid and reposition it closer to Earth. —ArsTechnica, 14 Apr. 2025

European Army and the EU The nebulous idea of a European military has long floated around, but mostly dismissed as impractical and unnecessary while NATO exists in its current form. —Daniel R. Depetris, Newsweek, 25 Mar. 2025

With only that nebulous countdown to rely on and sustained financing up in the air, the fledgling hypersonic sector certainly can’t afford to, well, cool its jets. —Michael Verdon, Robb Report, 22 Mar. 2025

Momentum has even seemed to shift in the area of litigation, where industry defendants have prevailed in a number of recent decisions in lawsuits brought by cities, counties, and states seeking billions in damage awards alleging nebulous damages due to greenhouse gas emissions. —David Blackmon, Forbes, 20 Mar. 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