head louse vs louse

head louse and louse both are nouns.

Word	Noun	Adjective	Verb	Adverb
head louse	Yes	No	No	No
louse	Yes	No	No	No

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

head louse: infests the head and body of humans
louse: wingless usually flattened bloodsucking insect parasitic on warm-blooded animals

Other hypernyms of head louse include sucking louse.

head louse (noun)	louse (noun)
infests the head and body of humans	wingless usually flattened bloodsucking insect parasitic on warm-blooded animals
	any of several small insects especially aphids that feed by sucking the juices from plants
	wingless insect with mouth parts adapted for biting; mostly parasitic on birds
	a person who has a nasty or unethical character undeserving of respect