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Glite Dictionary
to fog up

to fog up

9 2.8
Get covered with small drops of water that make glass or mirrors hard to see through
  • phrasal verb
  • /fɔg ʌp/
: empañarse
  • The cold air from outside made the car windows fog up quickly.
  • windows fog up
  • glasses fogged up
  • fogged-up mirror

Examples

  • She peers into the fogged-up bathroom mirror.

    Fiction book (1998)

  • It's so cold that my glasses are fogging up as soon as I get home.

  • It's making your windows fog up.

    Frozen River (2008)

  • The windows were all fogged up.

    Hollow Creek (2016)

  • The lenses of my glasses fogged up.

    Fiction book (1998)

  • The heater was on, but it was cold inside, and the windows fogged up right away.

    Fiction book (1999)

  • You're fogging up my glasses.

    Scooby-Doo (2002)

  • "Is it hot in here?" My glasses had fogged up, and I took them off to wipe them with my shirttail.

    Fiction book (1991)

  • She glanced away—anywhere, the floor, the fogged-up window—to keep from crying.

    Fiction book (1999)

  • Even on Sunday, Oct 14, when he finally made the jump, Baumgartner hit a small glitch prior to jumping when his helmet visor fogged up due to a broken heater.

    Blog text (14)

Synonyms

to fog
vsto fog up
15 5.2

To make something hard to see or understand

describes actual small surface droplets causing poor visibility rather than general obscuring
to mist
vsto fog up
3 3.1

To become covered with fine drops that make something less clear

focuses on small water drops forming on objects rather than general damp blurring
to haze
vsto fog up
1 4.7

To become cloudy and hard to see through

is specifically about tiny water drops covering surfaces and blocking sight
to mist over
vsto fog up
1 5.1

Become covered with a thin layer of water that makes glass or mirrors hard to see through

involves many small water drops forming on surfaces, not only a thin film
to haze over
vsto fog up
1 5.3

Look less clear as if covered by a thin mist

involves real small droplets forming on surfaces rather than an imagined haze

Antonyms

to defog
1 4.1

Remove fog from glass like car windows or mirrors

How Foggy

to fog up
9 2.8
to mist over
1 5.1
to haze over
1 5.3

Surface Forms

fog up infinitive
fogged up past
fogged up past participle
fogging up present participle
fogs up third person singular

Morphology

fog + up

The meaning is directly derivable from combining 'fog' (to make less visible/cover with mist) with the particle 'up' indicating becoming/bringing into that state; the phrasal-verb composition straightforwardly yields 'become covered with condensation'. This is a common and literal motion/state phrasal pattern in English (and has clear equivalents in many languages), so a B1 learner who knows the parts would readily understand it.

Etymology

The verb fog up comes from the simple picture of tiny water drops on glass: warm breath or steam makes the glass look like a thin fog, and the drops build up on the surface. That 'fog' makes the glass 'hard to see', so to fog up means to become covered and unclear.