nidus vs hornets' nest

nidus and hornets' nest both are nouns.

Word	Noun	Adjective	Verb	Adverb
nidus	Yes	No	No	No
hornets' nest	Yes	No	No	No

As nouns, hornets' nest is a hyponym of nidus; that is, hornets' nest is a word with a more specific, narrower meaning than nidus:

Other hyponyms of nidus include hornet's nest, wasp's nest, wasps' nest.

nidus (noun)	hornets' nest (noun)
a nest in which spiders or insects deposit their eggs	habitation for wasps or hornets
a central point or locus of an infection in an organism	a highly contentious or hazardous situation