German cockroach vs water bug

German cockroach and water bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
German cockroach	Yes	No	No	No
water bug	Yes	No	No	No

As nouns, German cockroach and water bug are synonyms defined as:

German cockroach and water bug: small light-brown cockroach brought to United States from Europe; a common household pest

Other synonyms of German cockroach include Blattella germanica, Croton bug, crotonbug.

German cockroach (noun)	water bug (noun)
small light-brown cockroach brought to United States from Europe; a common household pest	a true bug: large aquatic bug adapted to living in or on the surface of water
	small light-brown cockroach brought to United States from Europe; a common household pest