pruritus vs itchiness

pruritus and itchiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
pruritus	Yes	No	No	No
itchiness	Yes	No	No	No

As nouns, itchiness is a hypernym of pruritus; that is, itchiness is a word with a broader meaning than pruritus:

pruritus: an intense itching sensation that can have various causes (as by allergies or infection or lymphoma or jaundice etc.)
itchiness: an irritating cutaneous sensation that produces a desire to scratch

Other hypernyms of pruritus include itch, itching.

pruritus (noun)	itchiness (noun)
an intense itching sensation that can have various causes (as by allergies or infection or lymphoma or jaundice etc.)	an irritating cutaneous sensation that produces a desire to scratch