head lice vs lousiness

head lice and lousiness both are nouns.

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

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

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

Other hypernyms of head lice include pediculosis.

head lice (noun)	lousiness (noun)
infestation of the scalp with lice	the quality of being disgusting to the senses or emotions
	infestation with lice (Pediculus humanus) resulting in severe itching