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general::
Phrase(s): fog something up
to make something made of glass become covered with a film of water vapor. • The moisture fogged the windshield up, and we had to stop to clean it off. • The moisture fogged up the glass., Phrase(s): fog up
[for something made of glass] to become partially or completely obscured by a film of water vapor. • The glass fogged up, and we couldn’t see out.
McGrawhill's American Idioms And Phrasal Verbs