crab louse vs Phthirius pubis

crab louse and Phthirius pubis both are nouns.

Word	Noun	Adjective	Verb	Adverb
crab louse	Yes	No	No	No
Phthirius pubis	Yes	No	No	No

As nouns, crab louse and Phthirius pubis are synonyms defined as:

crab louse and Phthirius pubis: a louse that infests the pubic region of the human body

Other synonyms of crab louse include crab, pubic louse.

crab louse (noun)	Phthirius pubis (noun)
a louse that infests the pubic region of the human body	a louse that infests the pubic region of the human body