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

verb (used with object), fogged, fog·ging.

  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.
  3. to bewilder or perplex: to fog the mind.
  4. Photography. to produce fog on (a negative or positive).

verb (used without object), fogged, fog·ging.

  1. to become enveloped or obscured with or as if with fog.
  2. Photography. (of a negative or positive) to become affected by fog.

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.


  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

verb fogs, fogging or fogged

  1. to envelop or become enveloped with or as if with fog
  2. to confuse or become confusedto 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


    1. a second growth of grass after the first mowing
    2. grass left to grow long in winter

“thick, obscuring mist,” 1540s, probably from a Scandinavian source akin to Danish fog “spray, shower, snowdrift,” Old Norse fok “snow flurry,” fjuk “snow storm.” Cf. also Old English fuht, Dutch vocht, German Feucht “moist.” Figurative phrase in a fog “at a loss what to do” first recorded c.1600.


“long grass,” c.1300, probably of Scandinavian origin, cf. Norwegian fogg “long grass in a moist hollow,” Icelandic fuki “rotten sea grass.” The connection to fog (n.1), via a notion of long grass growing in moist dells of northern Europe, is tempting but not proven. Watkins suggests derivation from PIE *pu- “to rot, decay.”


1590s, from fog (n.1). Related: Fogged; fogging.

  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.

see in a fog.

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