pea-souper vs fog

pea-souper and fog both are nouns.

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

As nouns, fog is a hypernym of pea-souper; that is, fog is a word with a broader meaning than pea-souper:

pea-souper (noun)	fog (noun)
a heavy thick yellow fog	confusion characterized by lack of clarity
	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

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