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)

fogged, fogging

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)

fogged, fogging

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

   2. grass left to grow long in winter

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fog ² 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 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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Related Words

See cloud.

Other Word Forms

• fogless
  adjective
• unfogged
  adjective
• unfogging
  adjective

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

Women are now pursuing treatment for symptoms like hot flashes, brain fog, insomnia and dry, itchy skin.

From MarketWatch • May 12, 2026

Tuesday will begin on a chilly note, with any early fog soon clearing to leave sunny spells, but also a scattering of showers - most frequent across Scotland, northern England, the Midlands and Wales.

From BBC • May 4, 2026

Most of my wishlist was free, such as my Oura ring stats, San Francisco fog info and my local bus arrivals.

From The Wall Street Journal • May 3, 2026

The fog of war has taken away the visibility for the global economy at large and for individual countries.

From Barron's • May 1, 2026

The fog got still thicker, curling around Tiamat's feet like snakes made of smoke.

From "Jeremy Thatcher, Dragon Hatcher" by Bruce Coville

Related Words

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