pea soup vs soup

pea soup and soup both are nouns.

Word	Noun	Adjective	Verb	Adverb
pea soup	Yes	No	No	No
soup	Yes	No	Yes	No

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

pea soup: a thick soup made of dried peas (usually made into a puree)
soup: liquid food especially of meat or fish or vegetable stock often containing pieces of solid food

pea soup (noun)	soup (noun)
a thick soup made of dried peas (usually made into a puree)	liquid food especially of meat or fish or vegetable stock often containing pieces of solid food
a heavy thick yellow fog	an unfortunate situation
	any composition having a consistency suggestive of soup

pea soup (verb)	soup (verb)
	dope (a racehorse)