fog vs pea-souper

fog and pea-souper both are nouns.

Word	Noun	Adjective	Verb	Adverb
fog	Yes	No	Yes	No
pea-souper	Yes	No	No	No

As nouns, pea-souper is a hyponym of fog; that is, pea-souper is a word with a more specific, narrower meaning than fog:

Other hyponyms of fog include fogbank, ice fog, pogonip, mist, pea soup.

fog (noun)	pea-souper (noun)
confusion characterized by lack of clarity	a heavy thick yellow fog
droplets of water vapor suspended in the air near the ground
an atmosphere in which visibility is reduced because of a cloud of some substance

fog (verb)	pea-souper (verb)
make less visible or unclear