head lice vs pediculosis

head lice and pediculosis both are nouns.

Word	Noun	Adjective	Verb	Adverb
head lice	Yes	No	No	No
pediculosis	Yes	No	No	No

As nouns, pediculosis is a hypernym of head lice; that is, pediculosis is a word with a broader meaning than head lice:

head lice: infestation of the scalp with lice
pediculosis: infestation with lice (Pediculus humanus) resulting in severe itching

Other hypernyms of head lice include lousiness.

head lice (noun)	pediculosis (noun)
infestation of the scalp with lice	infestation with lice (Pediculus humanus) resulting in severe itching