A peasouper (very often written pea-souper) is a fog so thick you can barely see your own hand. British people named it after pea soup, which is dense and often a dull yellow-green; the joke is that the air looks good enough to eat, and just as hard to see through. The word is especially tied to old London, where wet air mixed with coal smoke and turned yellow-brown — those 'London peasoupers' were famous, and in the 1950s they made people ill, after which cleaner-air laws mostly ended that kind of smog. So the word is a little old-fashioned now, but people still use it, sometimes with a smile, for any fog that swallows the street. Informal British English; you would not put it in a science report. It is the weather, not a person.

濃霧（英式說法，濃得像豌豆湯；也特指舊時倫敦那種又黃又濃的霧）。