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

Common brain-related symptoms include fatigue, brain fog, memory problems, and low mood.

From Science Daily ● Sep. 22, 2026

There was no way, with my brain fog, I could have remembered everything my oncologists told me and having so much information-—including the visit summary notes-—in one place was an absolute lifesaver.

From The Wall Street Journal ● Sep. 17, 2026

There’s something in the fog — it’s Emmys history for Matthew Rhys.

From Los Angeles Times ● Sep. 15, 2026

She still struggles with fatigue, mental fog, memory loss and trembles if she becomes too exhausted, as well as suffering from regular dizzy spells.

From BBC ● Sep. 13, 2026

She turns the page and points at something else, but I don’t see it through the fog of tears clouding my vision.

From "Red Flags and Butterflies" by Sheryl Azzam

A fountain on the back patio roars, fogs and mists at patrons.

From Seattle Times ● May 31, 2024

For three solid, unrelieved weeks, the pileup of cyclonic storms has obscured the Northern California coastlines with dense drifting fogs and white mist thrown off huge waves.

From Washington Post ● Jan. 20, 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

My breath fogs out in giant puffs in front of me.

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

Then his visor fogged up and he couldn’t see.

From Seattle Times ● Mar. 18, 2024

“Well, then…” Frabwick leaned so close his breath more completely fogged Clare’s monocle.

From "The Undead Fox of Deadwood Forest" by Aubrey Hartman

Less than two years in, she started having daily asthma attacks, as well as headaches, dizziness, and rashes while her walls were sweating and windows were fogging up because of the humidity.

From The Wall Street Journal ● Aug. 24, 2026

"Instead of soil, we pack these containers with a specialized coco-peat substrate derived entirely from coconut husk. We then integrate a highly precise drip-irrigation and fogging system to control micro-climates."

From BBC ● Jul. 30, 2026

“As for fogging, we drilled holes in the plastic at the side of the nose and that worked.”

From Los Angeles Times ● Apr. 8, 2024

In older adults, such changes as loss of receptor cells in the ear and eye, fogging of the eye’s lens or loss of functioning in peripheral nerves, motion sickness may either increase or decrease.

From Scientific American ● May 26, 2023

His breath steamed in the air, fogging the ice behind his head.

From "A Dance with Dragons" by George R. R. Martin

Related Words

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