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
• cryptic
• obscure
• dark
• vague
• mysterious

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

This question is especially helpful if your energy feels scattered or you’re tasked with nebulous goals or shifting targets. —Cynthia Pong, Forbes.com, 13 July 2025

As massive young stars carve away at nearby gas and dust, their bright starlight produces a bright nebulous glow, represented in the image in blue. —Julia Jacobo, ABC News, 11 July 2025

His role within the White House has been nebulous and confusing. —Stephen Fowler, NPR, 30 May 2025

Also on the chopping block are cultural institutions that have dared to embrace any programs or offerings that fall under his nebulous and ever-expanding definitions of DEI, as well as institutions that don’t sufficiently toe the line. —New York Daily News Editorial Board, New York Daily News, 24 Apr. 2025

Word History

Etymology

Latin nebulosus misty, from nebula

First Known Use

1674, in the meaning defined at sense 1

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