giant water bug vs water bug

giant water bug and water bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
giant water bug	Yes	No	No	No
water bug	Yes	No	No	No

As nouns, water bug is a hypernym of giant water bug; that is, water bug is a word with a broader meaning than giant water bug:

giant water bug: large water bug with piercing and sucking mouthparts; feeds on young fishes
water bug: a true bug: large aquatic bug adapted to living in or on the surface of water

giant water bug (noun)	water bug (noun)
large water bug with piercing and sucking mouthparts; feeds on young fishes	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