English Reference

Word

nebulous

Phoneticsneb·u·lous

US/ˈnɛbjəɫəs/

UK/nˈɛbjʊləs/

Definitions

01vague or unclear

C1

adj. not clear or specific; difficult to describe or understand exactly.

adj. lacking definite form, limits, or content; vague or ill-defined in a conceptual sense.

“The company had some nebulous plans for the future, but nothing was written down.”

“The candidate's platform remained nebulous throughout the campaign, frustrating voters who wanted specific policy proposals rather than broad rhetoric.”

Academic · Formal

Usage

Commonly used to describe abstract concepts like ideas, plans, or memories.

02cloudy or hazy

C2

adj. looking like a cloud or a mist; not having a sharp edge.

adj. resembling a cloud or haze; lacking a clearly defined physical outline.

“A nebulous glow appeared in the sky just before the storm started.”

“Through the telescope, the scientist observed a nebulous mass of gas and dust where new stars were beginning to form.”

Literary · Technical

Usage

Often used in scientific contexts or descriptive literature to describe light or distant objects.

Synonyms

Antonyms

03relating to space nebulae

C2 · Science

adj. related to a nebula, which is a giant cloud of dust and gas in space.

adj. pertaining to or having the characteristics of a nebula.

“The astronomer spent years studying nebulous gases in the Orion constellation.”

“The paper discusses the chemical composition of various nebulous structures found within the Milky Way.”

Technical

Teaching tip

This is the most literal and technical sense of the word; most learners will encounter the 'vague' sense more frequently in general reading.

Real-World Examples

“It’s mind-blowingly vague and nebulous.” The “Hazelwood standard”, as it is now called, looms over cases such as Mountain View.”
The Guardian · 4 Sept 2026

Etymology

From Middle English, from Middle French nebuleus, from Latin nebulōsus (“full of mist, foggy, cloudy”), from nebula (“mist, vapour, cloud”), from Proto-Indo-European *nébʰos (“cloud, vapor, fog, moist, sky”). Cognates *Ancient Greek νέφος (néphos, “cloud”) *German Nebel **Old High German nebul (“cloud, fog”) *Old English nifol, neowol (“dark, gloomy, obscure, precipitous, prone”) by surface analysis, nebula + -ous. More at neveling, nuel.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Word family

nebulaNounnebulousAdjective

This entry

Level
C1 · Advanced
Frequency
Occasional
Updated

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