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

Your chatter zone lights up as the life-giving Sun conjoins nebulous Neptune, blending insight with curiosity for thoughtful conversations and local plans. —Tarot.com, Sun Sentinel, 22 Mar. 2026

Proton’s Global Network Triumphs Server counts can be nebulous, and these figures can change daily. —Justyn Newman, PC Magazine, 22 Mar. 2026

On top of these apparitions, a human foe, whose motives for committing a crime seem rather nebulous, also exists. —Carlos Aguilar, Variety, 15 Mar. 2026

Sadly, these cells are unable to detect color, so galaxies often appear as a nebulous halo of light surrounding a bright central core, occasionally featuring hints of dark, dusty lanes. —Anthony Wood, Space.com, 14 Mar. 2026

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