R.V. vs dune buggy

R.V. and dune buggy both are nouns.

Word	Noun	Adjective	Verb	Adverb
R.V.	Yes	No	No	No
dune buggy	Yes	No	No	No

As nouns, dune buggy is a hyponym of R.V.; that is, dune buggy is a word with a more specific, narrower meaning than R.V.:

R.V.: a motorized wheeled vehicle used for camping or other recreational activities
dune buggy: a recreational vehicle with large tires used on beaches or sand dunes

Other hyponyms of R.V. include camper, camping bus, motor home, beach buggy.

R.V. (noun)	dune buggy (noun)
a motorized wheeled vehicle used for camping or other recreational activities	a recreational vehicle with large tires used on beaches or sand dunes