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

The case relates to the treatment of people attempting to reach Europe who were intercepted by the Libyan Coast Guard (LCG) - which is a nebulous entity comprising forces of the Libyan Navy as well as militias and criminal groups - in 2017. —Frey Lindsay, Forbes.com, 17 June 2025

Her mother Sandy is her sole parent after her father passed away from some sort of nebulous accident, and Sandy has already been through it in the intervening years. —Kate Erbland, IndieWire, 10 June 2025

Ultimately, all of the queens performed pretty well this week, making the criteria seem extra nebulous depending on who the judges are talking to. —Chris Feil, Vulture, 30 May 2025

In De Palma’s hands, Ethan’s big-screen debut is a labyrinthine whodunnit in which truth itself is nebulous at best. —Will Harris, EW.com, 23 May 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