Definition

Verb (intransitive) To become covered or obscured with a layer of condensation, making it difficult to see through. This typically occurs when warm, moist air comes into contact with a cooler surface, such as a window, mirror, or pair of glasses.

Usage

The verb "fog up" describes the process by which a transparent surface becomes cloudy or misty due to condensation. It is most commonly used for car windows, bathroom mirrors, and eyeglasses. It is an intransitive phrasal verb, meaning it does not take a direct object; the surface that becomes foggy is the subject of the sentence.

Examples

• The car windows fogged up as soon as we got inside on the cold, rainy day.
• My glasses always fog up when I wear a mask.
• The bathroom mirror fogs up during a hot shower.

Advanced Usage

• Causative Use with "get": While "fog up" itself is intransitive, you can use the structure "get something to fog up" or "make something fog up" to indicate causing the action.
  • The steam from the kettle got my glasses to fog up.
• Adjectival Form - "fogged up": The past participle is commonly used as an adjective to describe the state of the surface.
  • I can't see; the windshield is completely fogged up.

Variants and Related Words

• Fog (verb): The single-word verb can be used transitively or intransitively with a similar meaning, though "fog up" is more specific and common for this context.
  • The humid air fogged the lens. (transitive)
  • The lens fogged. (intransitive)
• Mist up (verb): A near-synonymous phrasal verb, more common in British English.
  • The windows misted up.

Synonyms

• Steam up
• Cloud over (when referring to transparent surfaces)
• Become misty

Related Phrasal Verbs

• Clear up: The opposite process; when the condensation disappears and the surface becomes transparent again.
  • Turn on the defroster so the windshield will clear up.

Related Idioms

• (All) fogged in: An idiom describing an area, like an airport, that is enveloped in thick fog, preventing travel. This is related in imagery but refers to weather, not condensation on a surface.
  • Our flight was delayed because the airport was fogged in.

Verb

1. get foggy
   • The windshield fogged up