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

Good binoculars will reveal a score of stars in this little group, while long-exposure observatory photographs show about 1000 in the area — all suffused in great clouds and streamers of nebulous light. — Joe Rao, Space.com, 10 July 2026

Increasingly, the crux of the debate around AI’s sustainability has been focused on data centers, which make the nebulous concept of AI very concrete with their massive, humming warehouses full of servers and huge energy requirements. — Sasha Luccioni, Time, 3 July 2026

When college senior Sloane pursues a nebulous affair with her mysterious neighbor Ethan, the road to heartbreak ends up functioning as a path to self-discovery. — Nissa Renzo, PEOPLE, 30 June 2026

There are also more nebulous items, including advice to beware of social engineering. — Neil J. Rubenking, PC Magazine, 24 June 2026

Word History

Etymology

Latin nebulosus misty, from nebula

First Known Use

1674, in the meaning defined at sense 1

Podcast

Get Word of the Day delivered to your inbox!

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