water bug vs German cockroach

water bug and German cockroach both are nouns.

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

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

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

Other synonyms of water bug include Blattella germanica, Croton bug, crotonbug.

water bug (noun)	German cockroach (noun)
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
small light-brown cockroach brought to United States from Europe; a common household pest