volume unit vs yard

volume unit and yard both are nouns.

Word	Noun	Adjective	Verb	Adverb
volume unit	Yes	No	No	No
yard	Yes	No	No	No

As nouns, yard is a hyponym of volume unit; that is, yard is a word with a more specific, narrower meaning than volume unit:

volume unit (noun)	yard (noun)
a unit of measurement of volume or capacity	an enclosure for animals (as chicken or livestock)
	a long horizontal spar tapered at the end and used to support and spread a square sail or lateen
	the enclosed land around a house or other building
	an area having a network of railway tracks and sidings for storage and maintenance of cars and engines
	a tract of land enclosed for particular activities (sometimes paved and usually associated with buildings)
	a tract of land where logs are accumulated
	a unit of length equal to 3 feet; defined as 91.44 centimeters; originally taken to be the average length of a stride
	a unit of volume (as for sand or gravel)
	the cardinal number that is the product of 10 and 100