wood louse vs woodlouse

wood louse and woodlouse both are nouns.

Word	Noun	Adjective	Verb	Adverb
wood louse	Yes	No	No	No
woodlouse	Yes	No	No	No

As nouns, wood louse and woodlouse are synonyms defined as:

wood louse and woodlouse: any of various small terrestrial isopods having a flat elliptical segmented body; found in damp habitats

Other synonyms of wood louse include slater.

wood louse (noun)	woodlouse (noun)
any of various small terrestrial isopods having a flat elliptical segmented body; found in damp habitats	any of various small terrestrial isopods having a flat elliptical segmented body; found in damp habitats