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 otherworldly—after all, it’s related to nebula, which refers to 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 Teju Cole wrote of an avant-garde photographer who viewed photography as existing “neither in the camera nor in the printed photograph, but in a more nebulous zone.”

Synonyms of nebulous

• ambiguous
• cryptic
• obscure
• dark
• vague

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

Dictionaries duke it out for attention, some touting their scientific methodology for picking a winner, others offering a nebulous alchemy of number-crunching and feel. —Literary Hub, 13 Nov. 2025

While GPT-4o was a critical factor in the advent of spiralism, the faithful are hardly limited to this model, and have had success replicating elements of this nebulous framework with competitors including Gemini, DeepSeek, and Grok. —Miles Klee, Rolling Stone, 11 Nov. 2025

Republicans would separately make commitments to Democrats on health care, such as a vote in December on extending enhanced Affordable Care Act tax credits, though the details of those agreements remain nebulous. —Eleanor Mueller, semafor.com, 9 Nov. 2025

Bean acknowledged that measuring nebulous concepts like reasoning requires evaluating a subset of tasks, and that such selection will invariably be imperfect. —Jared Perlo, NBC news, 6 Nov. 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