fog

¹ American  

[fog, fawg] / fɒg, fɔg /

noun

1. a cloudlike mass or layer of minute water droplets or ice crystals near the surface of the earth, appreciably reducing visibility.

2. any darkened state of the atmosphere, or the diffused substance that causes it.

3. a state of mental confusion or unawareness; daze; stupor.

   The survivors were in a fog for days after the catastrophe.

   Synonyms:

   dim, darken, blur, cloud, trance, muddle, haze

   Antonyms:

   clarity

4. Photography. a hazy effect on a developed negative or positive, caused by light other than that forming the image, by improper handling during development, or by the use of excessively old film.

5. Physical Chemistry. a mixture consisting of liquid particles dispersed in a gaseous medium.

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verb (used with object)

• fogs,
  present (3rd person singular)
• fogged,
  past participle,  past
• fogging
  present participle

1. to cover or envelop with or as if with fog.

   The steam in the room fogged his glasses.

2. to confuse or obscure.

   The debate did little else but fog the issue.

   Synonyms:

   obfuscate, obscure, muddy, confuse, befog, becloud

   Antonyms:

   clarify

3. to bewilder or perplex.

   to fog the mind.

   Synonyms:

   befuddle, daze, mystify, muddle

4. Photography. to produce fog on (a negative or positive).

verb (used without object)

• fogs,
  present (3rd person singular)
• fogged,
  past participle,  past
• fogging
  present participle

1. to become enveloped or obscured with or as if with fog.

   Antonyms:

   clear

2. Photography. (of a negative or positive) to become affected by fog.

fog ² American  

[fog, fawg] / fɒg, fɔg /

noun

U.S. and British Dialect.

1. a second growth of grass, as after mowing.

2. long grass left standing in fields during the winter.

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fog ¹ British  

/ fɒɡ /

noun

1. a mass of droplets of condensed water vapour suspended in the air, often greatly reducing visibility, corresponding to a cloud but at a lower level

2. a cloud of any substance in the atmosphere reducing visibility

3. a state of mental uncertainty or obscurity

4. photog a blurred or discoloured area on a developed negative, print, or transparency caused by the action of extraneous light, incorrect development, etc

5. a colloid or suspension consisting of liquid particles dispersed in a gas

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verb

1. to envelop or become enveloped with or as if with fog

2. to confuse or become confused

   to fog an issue

3. photog to produce fog on (a negative, print, or transparency) or (of a negative, print, or transparency) to be affected by fog

fog ² British  

/ fɒɡ /

noun

1. 1. a second growth of grass after the first mowing

   2. grass left to grow long in winter

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fog Scientific  

/ fôg /

1. A dense layer of cloud lying close to the surface of the ground or water and reducing visibility to less than 1 km (0.62 mi). Fog occurs when the air temperature becomes identical, or nearly identical, to the dew point.

2. An opaque or semiopaque condensation of a substance floating in a region or forming on a surface.

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fog Idioms  

1. see in a fog.

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Synonym Usage

See cloud.

Other Word Forms

Derived Forms

• fogless
  adjective
• unfogged
  adjective
• unfogging
  adjective

Inflected Forms

Participles

• fogging
  present
• fogged
  past

Conjugated Forms

Present

• fog
  simple
• fogs
  simple
• have fogged
  perfect
• has fogged
  perfect
• am fogging
  progressive
• are fogging
  progressive
• is fogging
  progressive
• have been fogging
  perfect progressive
• has been fogging
  perfect progressive

Past

• fogged
  simple
• had fogged
  perfect
• was fogging
  progressive
• were fogging
  progressive
• had been fogging
  perfect progressive

Future

• will fog
  simple
• will have fogged
  perfect
• will be fogging
  progressive
• will have been fogging
  perfect progressive

Etymology

Origin of fog¹

First recorded in 1535–45; perhaps by back formation from foggy; see fog ²

Origin of fog²

First recorded in 1300–50; Middle English fogge, from Scandinavian; compare Norwegian fogg “long, scattered grass on damp ground”; further origin uncertain; see also foggy

Explanation

Fog is a hazy, cloudy layer of water vapor very that hovers close to the ground. Driving in fog feels a bit like being inside a cloud. Fog is just what it appears to be — a cloud lying low in the atmosphere, getting its moisture from a body of water like the ocean or a river. When fog is thick, it can be dangerous to drive in, and most cars have special "fog lights" to help drivers see the road. When you're deeply confused, you can call it a fog too, and when things are unclear (literally or figuratively), they're said to fog up."

Example Sentences

See Examples For:

fog fogs fogged fogging

A December day in Stalingrad in 1942: “The dark clouds shed their burden, then brightened and climbed higher into the sky. The fog froze, settling as a thick white powder on army telegraph cables.”

From The Wall Street Journal ● Aug. 10, 2026

"I feel so much better, more clarity, less brain fog and I feel so much more balanced."

From BBC ● Aug. 8, 2026

At first, she was in a state of shock, describing her mind as being in a fog.

From Los Angeles Times ● Aug. 8, 2026

Josh Smith, from Wrexham, began experiencing brain fog and headaches in January, but assumed he was "just tired".

From BBC ● Jul. 28, 2026

The moon lights a layer of fog on the lake.

From "The Bletchley Riddle" by Ruta Sepetys and Steve Sheinkin

The skyline’s angular visage melted away, as mists and fogs and silvery showers softened edge by edge.

From Seattle Times ● Sep. 28, 2023

Wolfe shatters the rhythmic unison of her singers with dense, overwhelming fogs of phrases that return to unity with new focus and force.

From New York Times ● Sep. 16, 2022

There is an iconic scene in "Jurassic Park" when a velociraptor's breath fogs up a window as it searches for its prey.

From Salon ● May 29, 2022

“It fogs up my glasses in cold weather,” he says.

From Washington Post ● Jan. 21, 2022

I’d rather be outside with the men, rounding up the goats and cooping the chickens for the night, feeling hot inside my coat from the effort as my breath fogs out in the cold.

From "The Wrong Way Home" by Kate O’Shaughnessy

Streetcars delivered residents to their errands across the city, windows fogged with condensation.

From The Wall Street Journal ● Jun. 12, 2026

One of the quiet tragedies of the potluck is that perfectly good food often remains trapped in its travel container — lids half removed, plastic corners fogged with condensation.

From Salon ● Mar. 15, 2026

Photos on social media showed them slouched on plastic chairs, swathed in plastic bags fogged up by their breath.

From BBC ● Oct. 2, 2025

And for several days, trial coverage was fogged by TV footage of campus protests.

From Los Angeles Times ● May 9, 2024

I think I started to breathe a little bit more quickly, since the glass fogged up and I had to wipe the wet away.

From "Okay for Now" by Gary D. Schmidt

It was closed and the glass was fogging up with condensation.

From BBC ● Aug. 3, 2023

Wearing a mask comes with some discomfort, including hindering communication and fogging up glasses.

From New York Times ● Feb. 1, 2023

Asked about that situation this week, Norton said he had forgotten the details, the passage of so many years fogging his memory.

From Los Angeles Times ● Aug. 20, 2022

It has no air conditioning and only a small fan in the helmet to keep the visor from fogging.

From Seattle Times ● Aug. 3, 2022

Her father squeezed her fingers and sighed, his breath fogging his spectacles again.

From "A Wish in the Dark" by Christina Soontornvat

Related Words

• cloud
• gloom
• smog
• smoke
• steam
• vapor